Content

Department of Philosophy   Northern Illinois University
Tomis Kapitan

Peirce and the Autonomy of Abductive Reasoning

Erkenntnis 37 (1992)

ABSTRACT. Essential to Peirce's distinction among three kinds of reasoning, deduction, induction and abduction, is the claim that each is correlated to a unique species of validity irreducible to that of the others. In particular, abductive validity cannot be analyzed in either deductive or inductive terms, a consequence of considerable importance for the logical and epistemological scrutiny of scientific methods. But when the full structure of abductive argumentation -- as viewed by the mature Peirce - is clarified, every inferential step in the process can be seen to dissolve into familiar forms of deductive and inductive reasoning. Specifically, the final stage is a special type of practical inference which, if correct, is deductively valid, while the creative phase, surprisingly, is not inferential at all. In neither is abduction a type of inference to the best explanation. The result is a major reassessment of the relevance of Peirce's views to contemporary methodological studies.
 
 
 

1. THE PROBLEM


Discussions of scientific discovery and justification commonly refer to

C. S. Peirce's threefold distinction among the basic kinds of reasoning:

abduction is the process of both generating hypotheses and selecting

some for further pursuit, deduction draws out their testable conse-

quences, while induction evaluates them (CP 5.171, 6.468-477).1 Be-

sides this difference of roles in the process of scientific inquiry, Peirce

added that reasoning within each kind utilizes distinctive methods or

forms, and that there are diverse senses in which these methods can be

described as valid or as legitimate means of extending our knowledge.

The latter is at the core of his contention that each kind of reasoning

is irreducible to the other two, specifically, that abduction is an auton-

omous branch of logic.

    While there is widespread agreement about the need to distinguish

between inductive and deductive correctness, there is less concerning

the autonomy of abduction, even when one follows Peirce in refusing

to label all ampliative reasoning as "inductive." The issue is not whether

there are the three kinds of reasoning Peirce delineated, each with its

characteristic aims and methods, nor whether abductive procedures

constitute a proper phase of scientific inquiry. The question of auton-

omy, as here understood, concerns the alleged irreducibility of abductive

correctness, for insofar as abduction is a characteristic method

of either discovery (Hanson 1958, Thagard 1988) or explanation (Ach-

instein 1972, Boyd 1984), it is this claim that carries a truly significant

logical and epistemological import in the study of scientific method.2

How did Peirce defend the autonomy of abduction? A common

assumption is that abduction is unique in its generative capacity (CP

5.171), yet Peirce complicated matters by describing a twofold process

of both discovery and pre-testing preference:
 

The first starting of a hypothesis and the entertaining of it, whether as a simple

interrogation or with any degree of confidence, is an inferential step which I propose to call

abduction. This will include a preference for any one hypothesis over others which would

equally explain the facts. (CP 6.525)
 


In which phase does the irreducibility of abduction lie, in discovery

or preference? Either choice raises problems; despite the conceptual

distinctions, it is difficult to demarcate the reasoning involved in hypo-

thesis-preference from the deductive and inductive strategies used to

evaluate hypotheses (Thagard 1981, p. 258), and there is serious doubt

that Peirce developed a distinctive logic of discovery (Laudan 1980,

p. 174; Foss 1984, p. 30; Brown 1988, p. 404). From whence, then,

autonomy?

    To avoid debating a position Peirce himself did not hold, the issue

must be addressed with reference to his overall views on inference and

validity. But when this is done, there remains little to secure the auton-

omy of abduction, since a close analysis of his writings reveals,

(A) valid abductive reasoning does not sanction inference to a

novel hypothesis (specifically, abduction is not inference to

the best explanation);

(B) the initial conceiving of a novel hypothesis is not the product

of an inferential transition;

(C) both discovery and preference embody special sorts ot practi-

cal reasoning which justify, not belief, but adoption of a

course of action;

(D) every inferential phase of the abductive process can be ana-

lyzed in terms of inductive or deductive methods;

(E) there is no abductive correctness that cannot be reduced to

deductive or inductive validity.3

If these hold, as I shall argue they do, then "abductive" methods for

generating and preferring hypotheses fail to be autonomous from either

a logical or an epistemological point of view.

    The result is significant, and not only out of concern for historical

accuracy. Peirce's ideas about method have had a substantial impact

upon the contemporary philosophy of science, and a proper assessment

of their relevance demands clarity about their precise nature and

strengths. If claims (A)-(E) are correct, then the inferential procedures

characterizing abductive discovery do not transcend deductive or induc-

tive methods (Pera 1980, 1987, Zahar 1983), while the heuristic strat-

egies that do are not rules of inference. As regards preference, abduc-

tion does not provide a unique means for conferring evidence, and

there is doubt that Peirce took it as evidential reasoning at all; evidence

and hypothesis-confirmation are a matter for the joint operation of

deduction and induction. In particular, abduction is not inference to

the best explanation, in which case its relevance does not depend upon

the plausibility of that, admittedly controversial, mode of reasoning

(see note 2).

    Apart from impact, Peirce's theory of abduction carries an indepen-

dent interest, and not just for the reasons usually given, i.e., that

discovery involves rational processes, or that abductive reasoning is

distinct from deduction and induction. If the following interpretation

is accurate, then the study of scientific method ought not be exhausted

by scrutiny of evidential, intra-theoretical, and inter-theoretical re-

lations among propositions; it must also concern itself with the conduct

of inquiry and, consequently, with procedures for evaluating inferences

to practical directives. It is the practical character of abductive reason-

ing, specifically, its inference from a "best explanation" to a directive,

that makes Peirce's account of scientific method both novel and instruc-

tive.
 

2. INFERENCE AND VALIDITY

According to Peirce, an inference is "the conscious and controlled

adoption of a belief as a consequence of other knowledge," (CP 2.442,

2.144, 5.109) which "consists in the thought that the inferred conclusion

is true because in any analogous case an analogous conclusion would

be true" (CP 5.130). Its aim is "to find out, from the consideration of

matters and things already known, something else that we had not

known before" (MS 628:4), thus, to increase our grasp of truth. The

occurrences of 'as a consequence of and 'because' in these passages

not only indicate a premise-conclusion relation, but carry a causal

significance since inference "produces" or "creates" a belief in the

mind of the reasoner (CP 2.148). A belief, in turn, is described as a

"holding for true," or "any kind of holding for true or acceptance of

a representation" (NEM 4, 39-40), and "to say we really believe in

the truth of any proposition is no more than to say we have a controlling

disposition to behave as if it were true" (MS 652:15).4

    These characterizations pose a problem, for Peirce also contended

that abduction is not a matter for belief (CP 5.589), that belief is out

of place in science (CP 5.60, 1.635), and that non-truth-valued items

like questions can follow logically from antecedent information (MS

293:37). Conveniently, he also spoke of inference in terms of accept-

ance, a broader type of "favorable attitude towards" a proposition with

which positive belief was sometimes contrasted (MS 873:23). While not

productive of a full-fledged belief, an abduction still results in a type

of acceptance, though it is another matter to determine what particular

modes of acceptance there are. Recourse to this broader notion is

essential in achieving a general definition of inference, though it cannot

yet be ruled out that all acceptance is ultimately belief of one sort or

another (CP 7.102).

    Three steps are essential to any inference: colligation, observation,

and judgment (MS 595:35). Inference begins with colligation, the con-

joining of distinct propositions and asserting the whole (CP 2.442-3,

5.579). One then deliberately contemplates the colligated data (MS

595:30, CP 7.555) which, in turn, results in an observation that some

proposition C will hold if the single colligated premise P does. Next

follows a judgment which embodies first, an acceptance that what is

observed in the premise yields, by following a rule, the proposition C

and, second, an acceptance of C itself (CP 7.459, 2.444, 1.606). Control

is exercized over colligating, contemplating, and both phases of judg-

ment, but not over the observing (CP 7.555).

    Because it is controlled, an inference can be subjected to rules or

norms indicating what one would be warranted in accepting. Since

norms are appropriate only in relation to ends (CP 5.594), then follow-

ing the appropriate inference rules helps us to realize the end of reason-

ing, namely, acquisition of truth, a goal which we are justified in both

presuming can be reached and, therefore, in pursuing (MS L75:271).

An inference is valid if it is conducive to such acquisition, more pre-

cisely, if it follows a method (norm) which (i) it professes to follow,

and (ii) has the truth-producing virtue it is supposed to have, i.e., qua

being an inferential method of one of the three elementary kinds (CP

2.780).5   In this way, Peirce effectively extended the concept of validity

beyond both the deductive ideal of truth-preservation and the inductive

standard of likelihood, to that of truth-productivity. We must do so if

we hope to expand our grasp of truth, he thought, for deductive and

inductive reasoning are insufficient in their generative capacities.

    There are three ways in which inferential methods can be truth-

producing: a method is deductively valid insofar as it invariably (neces-

sary deduction), or very probably (probable deduction), yields truth

from truth: inductively valid if by following it we approximate to the

truth in the long run, and abductively valid insofar as it leads to truth

if truth can be attained at all (CP 2.781, 5.161). Analogously, one

might refer to the assurance that a given method is truth-producing:
 

the distinction that is undoubtedly of highest importance . . . is that which consists in the

nature of the assurance being different. (MS L231:56)


Two dimensions of assurance are invoked at this point; security and

liberty. Security is a measure of the confidence that we are avoiding

falsehood in the inferential transition, while uberty reflects the pro-

ductiveness in knowledge gained, i.e., that we are increasing our grasp

of truth. While we lose in security in moving from deduction to induc-

tion and, again, in going to abduction, we gain in uberty at each step

(CP 8.384-8).6

    Yet these distinctions do not, by themselves, establish the autonomy

of abduction. The matter cannot be settled by agreeing that there are

inferences, inferential patterns, or methods of reasoning which are

abductively valid. Perhaps all "logically good" inferences or inference

methods are, since abductive goodness is but the weakest assurance of

having reached truth. What must be shown is that there are some

modes of valid inference which can be justified only abductively, for

unless there are, Peirce's claim to have unearthed an irreducibly third

mode of reasoning cannot be substantiated. The claim for autonomy

requires a supporting existence proof.
 
 

3. DISCOVERY, PREFERENCE, AND ABDUCTIVE FORM

Recalling that Peirce understood 'abduction' to encompass logical-

mechanisms for both generating hypotheses and selecting certain of

them for further examination, let us speak of "abductive-discovery"

and "abductive-preference" respectively.

    He supplied different models of abductive form, the most character-

istic being that presented in his 1903 lectures on Pragmatism:
 

(Fl) (1) The surprising fact, C, is observed;

       (2) If H were true, C would be a matter of course.

       Hence,

       (3) There is reason to suspect that H is true.7


At one level of abstraction, the premises accurately portray scientific

procedure; research typically begins with a problem (puzzling or surpris-

ing phenomenon) and aims at a solution in terms of an explanatory

hypothesis. Yet, from the standpoint of valid reasoning (Fl) is problem-

atic. There are any number of "wild" hypotheses that would explain

why I am now reading this paper, but that alone does not provide

reason to think that any particular one is true (Achinstein 1970, p. 92).

More is required to legitimately conclude, select, or make plausible a

hypothesis than what (Fl) reveals and, if anything, the "logic" of

abduction should bring this out.

    Peirce did offer more. Keenly aware that there are numerous hypoth-

eses which would explain any given fact were they true (CP 5.591), he

viewed it as a "serious problem" whether a given hypothesis should be

entertained at all (CP 6.524). Using the label of 'economy' (MS

L75:284, CP 7.218-23), he claimed that the abductive inference to

hypothesis H is justifiable only if H is economical, or, better, more

economical than competing hypotheses. If so, an accurate rendition of

abductive form needs a further premise, viz.,
 

(F2) (1) Some surprising fact Cis observed.

        (2) If H were true then C would be a matter of course.

        (3) H is more economical than the envisioned competitors.

       Hence,

       (4) There is reason to suspect that H is true.


    This form qualifies as a type of inference to the best explanation

(Achinstein 1980, p. 126) but, as such, is more suitable as a format

for abductive-preference than abductive-discovery. Not only does the

hypothesis itself fail to be the conclusion, it appears twice in the prem-

ises, once as an antecedent and once as a subject of predication. Given

Peirce's causal account of inference, conception of H could not originate

as a product of an (F2)-inference (or, for that matter, of an (Fl)-

inference), nor can the reasoner's transition from its premises to its

conclusion be the moment of creative insight (Frankfurt 1958, 594).

This is especially apparent given the added premise, for the reasoner

could not legitimately accept it without a considerable familiarity with

the hypothesis.8
 
 
 

4.. ABDUCTIVE-DISCOVERY AND THE GENERATION OF THE PREMISES

(F2) represents a later stage of abductive thinking; before selecting a

hypothesis one must first come up with the surprising fact, formulate

explanatory conditionals, and assess rival explanations. Noting that

Peirce took scientific abduction to include all the operations whereby

theories are engendered (CP 5.590), we will first inquire whether the

autonomy of abduction is to be located in its earlier stages,

    Abductive thinking begins by juxtaposing the unfamiliar with the

familiar (MS L75:286-7, CP 7.188). The claim that a phenomenon is

surprising is intelligible only against a body of background expectations,

for an isolated fact, not contrary to what is expected, calls for no

explanation at all (CP 7.192-201). The judgment that a phenomenon

is surprising is subsequent to the observation that it is contrary or

improbable given what is expected (MS L75:177, CP 2.776, 7.188-200),

hence, in need of explanation. But this judgment itself results from an

inference to a novel proposition, viz., it represents a "discovery" with

which scientific knowledge begins (CP 7.188).

    What kind of reasoning is involved? Colligation qua conjoining, is

deductive. Observation of what is contrary or improbable given what

is expected, comes by focusing upon the relations between premises

and conclusion. To "see" that P is contrary to Q or improbable given

Q, is to realize that either implies or makes likely ~P, in which case

the observation underlying a judgment of contrareity is exactly the sort

that typifies deduction. Hence, the inference that the phenomenon is

surprising, in want of explanation, appears to be deductive.

    It is upon judging that the surprising fact C would be explained by

a novel hypothesis H that the more familiar phase of creative thinking

emerges. A breach of expectation stimulates a demand for explanation

(CP 7.191) which, if successful, results in acceptance of an explanatory

conditional. However, it is doubtful that Peirce held the initial conceiv-

ing of H qua antecedent to arise as a result of inference. He wrote that

the abductive suggestion comes to us "like a flash," of its being an act

of "instinctive insight" tending to make us guess correctly nature's laws

(CP 5.604, 5.181), of abduction itself as being "neither more nor less

than guessing" (MS 692:24), and of a guessing as being an instinctive

power (CP 6.491, 7.48). On the other hand, he emphasized that one

guesses on the basis of other information (MS 692:27-36, 595:37); we

separate "reasonable" guesses from poor ones (MS 873.11), and given

that there are "trillions" of possible hypotheses to explain given facts,

we need the operation of rational constraints warding us away from

idle and fruitless guesses (CP 5.172, 5.591, 7.38). Hypotheses are not

generated fortuitously; guessing is an inferential process, as such, under

our control and not a purely instinctive affair (MS 475:20, CP 7.48,

6.476).9

    Peirce attempted to resolve this tension between instinct and control

in his 1903 Pragmatism lectures where he distinguished between emer-

gence of the novel hypothesis and inferential acceptance of its explana-

tory role. He claimed that the initial awareness of the hypothesis comes

with the observation of the colligated whole by means of an uncon-

trolled insight into the world of ideas, i.e., into what he called "Third-

ness" as given in perception (CP 5.150-212, 7.198). The novel conceiv-

ing of any instance of premise (2) of (F2), for example, is caused by

prior cognitions, its content is "suggested" by the facts, but not every-

thing suggested is inferred from cognition of the facts:

 
There are, as I am prepared to maintain, operations of the mind which are logically

exactly analogous to inferences excepting only that they are unconscious and therefore

uncontrollable and therefore not subject to criticism. (CP 5.108)


However, while such operations are "associational suggestions of belief,"

not "inferences" (CP 5.441, MS 1134), they can still be rule-governed

methods of originating hypotheses. Though Peirce offered

little by way of a logica docens in this regard, he was very much

concerned with heuristics of discovery (CP 2.105-7, NEM 4:196), as

evidenced by his account of theorematic reasoning, his insistence on

the "diagrammatic" character of mathematical thinking (NEM 4:46-9),

and his emphasis upon analogical thinking in the expansion of

knowledge:
 

Nothing unknown can ever become known except through its analogy with other things

known. Therefore, do not attempt to explain phenomena isolated and disconnected with

common experience. (MS L75:286)


An explanatory conditional, for example, might be generated by appli-

cations of the following Newtonian rule; a surprising fact C is like

another fact C' which is explained by hypothesis H'; thus, an H'-like

hypothesis H might explain C. As with other sorts of heuristic strategies,

use of this rule can stimulate those novel conceptions which, in turn,

spawn new inferences and the development of theories.10

    According to this view, heuristic strategies are not rules of inference

appropriate to controlled reasoning after novel conceptions have occurred, for inference requires seeing that the conclusion is justified

(MS 293: 7-8). While they are rules governing transitions from one

conception to another, they are typically stated in terms of what to

"look for," how to "express" something (Langley et al., 1987, p. 53),

what to "combine" or "find" (Thagard 1988, p. 202), not what to

"infer." They are aids in locating novel ideas, strategies for discovery,

hence, practical directives, but not formulae specifying what we are

entitled to accept. Nor do they correspond to principles for conferring

epistemic warrant, in which case their epistemological significance is of

a different order from that characterizing valid inference forms. In strict

Peircean terms, the emergence of hypotheses is not a matter of inference

and, therefore, not a matter of a unique form of inference.11

    As indicated in Section 2, an inference occurs only when the reasoner

exercises self-control in judging that the conclusion is acceptable on the

basis of the information one began with. In itself, such self-control is

purely "inhibitory" and "originates nothing" (CP 5.194), that is, the

creative moment lies with the instinctive observation that given what

one already knows, H will explain C. The correlated guess, the "deliber-

ate acceptance" (MS 451:18), is the reasoned adoption of the explana-

tory conditional, hence, it is a result of inference.

    This acceptance can be justified deductively; the very phrase "as a

matter of course" in premise (2) indicates a degree of intuitiveness, a

point underscored by the fact that explanatory conditionals convey a

connection of necessity or high probability (CP 8.231 and 7.36). This

claim is strengthened by Peirce's contention that once a hypothesis has

been identified, it is a matter of deduction to establish further con-

ditionals in which the hypothesis is the antecedent and predictions are

the consequents (CP 7.115n and MS 473:9-10). Ideally, among these

predictions will be those whose very "incredibility" makes their conse-

quents similar to the surprising fact C, in which case the inferential

acceptance of the explanatory conditional results by a deductive transi-

tion from the background assumptions.

    Concerning the third premise of (F2), finally, several considerations

must be taken into account before a hypothesis may be "chosen" for

further examination (CP 7.219). Obviously, it must be explanatory if

true and testable (CP 7.220), but under the heading of 'economy' Peirce

also included (a) the cost (in time, money, and effort) of testing the

hypothesis (CP 6.533, 7.230); (b) the instrinsic value of the hypothesis

in terms of its "naturalness and "likelihood" (CP 7.223); (c) the fact

that the hypothesis can be readily broken down into its elements and

studied (MS 692:33); (d) the hypothesis' simplicity (i.e., that it is more

readily apprehended, more facile, more natural or instinctive) (MS

L75:286, CP 6.532, 6.477): (e) the breadth of the hypothesis or the

scope of its predictions (MS L75:241; 457:37); (f) the ease with which

the hypothesis can be falsified (MS L75.-285); (g) the testability of the

hypothesis by means of severe tests based on "incredible" predictions;

and (h) the hypothesis' analogy with familiar knowledge (MS 873:16).

    The evaluations that emerge are comparative, often phrased in terms

of preference, in which case a judgment of economy is itself compara-

tive, as already suggested (CP 7.220-231, 2.786, NEM 4.37-8, MS

L75:285-6, and MS 475.37). The underlying inferences are best scrutin-

ized by means of the standard logic of preference in which deductive

considerations abound, especially in eliminating hypotheses by means

of disjunctive syllogisms (CP 7.37). But the reasoning to the premises of

any such deduction are likely to be inductive, in the mode of qualitative

inductions (CP 2.759, 7.209-217). How do we know, for instance, if

H is more cheaply testable than H"? We consider the kind of hypothesis

that // is, and based on our familiarity with past testing procedures,

we reason inductively that // is the kind of hypothesis that could be

examined more cheaply, more quickly, etc. Similar inductive consider-

ations would permeate decisions based upon the other criteria as well.

    Having argued that the reasoning used in generating the premises of

(F2) is either deductive or inductive, there are grounds for concluding

that the alleged irreducibility of abduction cannot be found therein. In

particular, it cannot be anchored in the process of abductive-discovery.

Accordingly, our examination of autonomy must return to abductive-

preference.
 
 
 
 

5. THE PROPER FORM OF ABDUCTIVE-PREFERENCE

A more rigorous scrutiny of (F2) is needed to ascertain whether a

unique kind of reasoning is manifested in abductive-preference. There

is an initial problem in that its conclusion is still too strong if interpreted

as conferring a high degree of probability to the hypothesis //, and too

weak if the probability is low. At any rate, probability is not the quality

which abduction aims at securing:
 

By its very definition abduction leads to a hypothesis which is entirely foreign to the

data. To assert the truth of its conclusion ever so dubiously would be too much. (MS

692:26, and see CP 2.102)


Exploring other conclusion-types, Peirce came to favor the view that

abductive-preference allows, at best, an inference to the "plausibility"

of the hypothesis:
 

By Plausible, I mean that a theory that has not yet been subjected to any test, although

more or less surprising phenomena have occurred which it would explain if it were true,

is in itself of such a character as to recommend it for further examination or, if it be highly

plausible, justify us in seriously inclining toward belief in it, as long as the phenomena be

inexplicable otherwise (CP 2.662)
 

Thus, a hypothesis is plausible if it is both explanatory and of a character

to recommend it for further examination (hence, testable, though un-

tested), noting that plausibility comes in degrees (see also CP 8.223,

6.469, 6.480-8). If it is plausibility, not truth, that we mean to establish

in hypothesis-preference, then the abductive conclusion should be "H

is plausible" (MS 652:16, Thagard 1981). This is fine so long as the

comparative nature of judgments of economy is reflected, i.e., the

warranted judgment is that // has a higher degree of plausibility, hence,

more to recommend it, because it is more economical. Making this

explicit yields the following form:
 

(F3) (1) Some surprising fact C is observed.

        (2) If H were true then C would be a matter of course.

        (3) H is more economical than its envisioned competitors.

        Hence,

        (4) H is more plausible than its envisioned competitors.12

Given what Peirce meant by 'plausible', this form of abduction-prefer-

ence is more faithful to his statement that the purpose of abduction is

"to recommend a course of action" (MS 637.5).

    But a striking feature of (F3) and the variant whose conclusion is "H

is plausible," is that they seem deductively valid; how could H fail to

be more plausible if it is explanatory, testable, and more economical

than its competitors (Achinstein 1970, p. 101)? One of Peirce's strat-

egies for determining the presence of deductive validity is to ask

whether the relevant leading principle is necessarily true, in this case,
 

(LI)   If  H is the most economical explanation of surprising phenomenon C,
         then H is more plausible than any of its competitors.
 
Given Peirce's definitions, this conditional appears to be a necessary

truth. Being the most economical explanation, H is obviously explana-

tory, testable, and therefore -- assuming considerations of economy to

be the proper basis for deciding the pre-testing merit of a hypothesis

-- to be recommended for further examination. Even when H has

comparatively little to recommend it, if there are no better competitors

we are nonetheless justified in putting it to test. In short, the judgment

seems irresistible that insofar as (F3) is a valid pattern at all, it is

deductively valid.

    It does not follow that it permissible to deductively infer H itself

from the (F3)-premises; no standard deductive (or inductive) canons

sanction such a conclusion. Yet, an inference to H might have been

what Peirce had in mind in insisting that abductive validity is unique,

and, if so, (F3) would not be what he envisioned as the proper form

of abductive-preference after all. This possibility must now be explored.
 
 
 

6. ABDUCTIVELY INFERRING THE HYPOTHESIS

Peirce frequently spoke of a hypothesis itself being "adopted" as a

result of an abduction, albeit "problematically" (CP 2.777) or "on

probation" (MS 873:22). A special mode of acceptance is operative

here (MS 638:5), a "probationary" mode which, falling short of belief

in the hypothesis (CP 5.60, 5.589) is still a favorable attitude towards

it (MS 873.23). It is the third and least assured of attitudes sanctioned

by the basic types of reasoning; full belief or positive assertion is

warranted in deduction (MS 473:17-18), provisional acceptance in in-

duction (CP 2.731; 5.591), and probational adoption in abduction. As

such, the correct pattern of abductive-preference might well be the

following extension of (F3):
 

(F4) (1) Some surprising fact C is observed.

        (2) If H were true then C would be a matter of course.

         (3) H is more economical than the envisioned competitors.

         Hence,

         (4) H is more plausible than its envisioned competitors.

         Hence, probationally,

         (5) H.


    Judging from appearances, we have returned to a type of inference

to the "best" explanatory hypothesis, and, with it, to a form that is not

readily classified as deductive or inductive. For Peirce, the qualifier

'probationally' indicates that justification belongs not to the sort of

acceptance warranted by valid deductive or inductive reasoning, but to

probational adoption only, where the latter is the acceptance which

culminates the entire abductive process. That (F4) is not a valid deduc-

tive or inductive schema is also suggested by the fact that instances of

the leading principle,
 

If H is more plausible than its envisioned competitors then H.


not only lack necessity but are typically false. The same is true of any

conditional linking the premises of (F4) to the probability of H, for

there is no assurance of approximating truth in the long run by its

means. On the surface, then, it would appear that insofar as (F4) is a

"valid" at all, its validity is of some third sort, perhaps an irreducible

"abductive" validity,

    Have we our desired existence proof? No, not until we clarify what

sort of "acceptance" probational adoption might be. While Peirce was

reluctant to say that abduction results in belief, he wrote that pro-

bational adoption involves some sort of favor extended to the hypo-

thesis. Perhaps the attitude stands to plausibility as belief does to truth,

i.e., it is to hold H to have, not truth, but a comparatively high degree

f plausibility (CP 2.776). This is one way to interpret his claim that a

hypothesis "... is accepted only problematically, that is to say, as

meriting an inductive examination" (CP 2.786), or, again, the following

passage:
 

It is one act of inference to adopt a hypothesis on probation. Such an act may be called

an abduction. It is an act of the same kind, when a hypothesis is merely suggested as

possibly worth consideration. For even then some degree of favor is extended to it. But

when, in consequence of having found that a good many predictions based on the

hypothesis have been verified, a man begins to have a positive beliefin it, that is an act

of inference of a totally different kind: it is an induction, or reasoning from a sample.

(MS 873.23)13


Given the normative character of plausibility, accordingly, accepting a

hypothesis as plausible is not to believe /;, rather, that it ought to be

pursued. The problem to be faced, however, is that if this were so,

then the transition from (4) to (5) in (F4) would be redundant inasmuch

as it would duplicate what one is already warranted in doing in moving

to step (4). The result would be to bring us back to (F3) and a straight-

forward deductive construal of abduction.

    Keeping probational adoption of H distinct from the beliefs thatH

that H is plausible, or that H ought to be pursued, leaves the possibility

that it is a practical attitude of willingness, resolve (CP 5.538), or

resolution (CP 1.592) to submit H to further test. This would amount

to a more literal reading of his previously-noted claim that the purpose

of an abduction is to "recommend a course of action," that is, endorsing

a recommendation to examine H is, just that, a "recommending,"

yielding a clear sense in which the abductively extended "favor" is

distinct from belief. Recommending or resolving to examine H, though

an explicit "endorsing" of a line of conduct (CP 5.538), is, at the same

time, a favorable attitude towards H itself - not the "controlled and

contented" disposition to act that belief in H would be (NEM 4.249),

only a readiness to submit H to testing, an attitude not accorded other

rejected hypotheses.

    There is still a difficulty; if abductive-preference is a special type of

practical reasoning, which culminates not in an acceptance of Hper se,

but in an endorsement of a course of action, then there is no distinction

between probationally adopting H and recommendinga further exami-

nation of H. Whatever warrant is conferred by the premises of (F4),

accordingly, reduces to the warrant for a decision, and, in strict terms,

the proper conclusion is not H, but a claim recommending H for further

examination. Therefore, abduction confers no epistemic warrant upon

the assertibility of H, and (F4) turns out to be a misleading representation of pre-testing selection.

    This somber assessment of (F4) is based on the inability to find a

straightforward doxastic interpretation of probational adoption within

Peirce's writings. It can be supported, however, by appeal to his pragmatic

criteria for identifying conceptions, for these dampen even further prospects

of demarcating acceptance on probation from practical resolve. Belief in a

proposition establishes behavioral habits and anchors expectations about one's

responses to its presumed consequences in a way that a mere decision to test it

does not. An investigator might have good grounds for thinking H to be worth

testing, yet have very good inductive grounds for being skeptical of H's success,

hence, be justified in granting it very little favor, even to the point of believing its negation

instead. Abductive-preference favors bold, though unlikely, conjec-

tures, and inductive warrant is no measure of the plausibility it confers.

Admittedly, Peirce's texts are not decisive; the foregoing is itself a

"hypothesis" as to what he might have meant. The proper conclusion

might be that he lacked a clear and consistent picture of what is to be

inferred in an abduction, or, for that matter, a clear distinction between

belief and other practical attitudes.
 

7. ABDUCTION-PREFERENCE AS PRACTICAL INFERENCE

If (F4) fails, yet (F3) offers little hope for the thesis of autonomy, what

other form of abductive-preference can we look to? Perhaps Peirce's

insistence that abduction aims at recommending a course of action

deserves a closer look. For instance, how is a recommendation sanc-

tioned once we have established that H is more plausible than its

competitors? From his definition of plausibility, we would immediately

have,
 

(a) There is reason to suppose that H is worth examining further.


But this falls short of an explicit directive; if a plausible theory has a

character to "recommend it for further examination," what is needed

is something stronger than a claim that there is "some" reason, or

"prima fade" grounds for so doing (Curd 1980, p. 214, and Achinstein

1987, p. 433). To capture the sense in which the hypothesis "merits"

inductive examination (CP 2.786, 8.223), a normative is more forceful:
 
 

(b) One ought, insofar as one desires an explanation of C, to examine H further.


or, alternatively,

 
(c) It is permitted, insofar as one desires an explanation of C, to examine H further.


Given the end of gaining truth, either of these is a proper manner of

asserting justification for hypothesis pursuit, since "ought" has no

meaning except relative to an end (CP 5.594).

    Although normatives like (b) or (c) can be used to support a practical

directive, e.g., a recommendation, neither is identical to a directive.

To make explicit the sense in which an abduction "recommends,"

something like the following must be sanctioned:
 

(d) H is recommended for further examination.


or, more carefully,
 

(e) It is recommended, for one who desires an explanation of C, to further examine H.


Obviously a recommendation is not a truth-valued declarative (Cas-

taneda 1975, Belnap 1990); in particular, (e) must not be confused with

a declarative report to the effect that someone or other has recom-

mended that H be further examined. Again, a recommendation can be

phrased interrogatively, and since Peirce often claimed that the hypo-

thesis should be asserted only as an "interrogation," implying by this

that the hypothesis merits testing (MS 692:26), the abductive conclusion

might be,
 

(f) Why not pursue H7


addressed to oneself or others. Or, phrasing the hypothesis itself inter-

rogatively (say, through the appropriate "wh-movements" of the gram-

marians), practical import can also be conveyed by,
 

(g) W


together with appropriate stress. Each of (d)-(g)are suitable Peircean

forms of practical directives, though, adhering to the letter of what was

said about the aim of scientific abduction, the schematic (e) will be

treated as canonical.

    A strict reading of Peirce suggests that abductive-preference requires

an explicitly "practical" inferential pattern formed by adding to (F3) a

second practically-oriented conclusion. What we come up with is an

argument form that qualifies not as inference to a best explanation.

but, as inference from the fact that a certain hypothesis is the best

explanation to a directive:
 

(F5) (1) Some surprising fact C is observed.

        (2) If H were true then C would be a matter of course.

        (3) H is more economical than its envisioned competitors.

        Hence,

        (4) H is more plausible than its envisioned competitors.

        Hence,

        (5) It is recommended, for one who desires an explanation

         of C, to further examine H.


To capture the normative aspect of plausibility, the actual chain ol

reasoning might also include either (b) or (c) between steps (4) and

(5). Perhaps Peirce had something close to (F5) in mind when he wrote

that abduction "commits us to nothing. It merely causes a hypothesis

to be set down upon our docket of cases to be tried" (CP 5.602). The

phrases "to be set down" and "to be tried" more closely reflect a

decision concerning future action, thus, a resolve about how to act. To

this extent, abductive-preference is a species of practical reasoning.14
 
 
 

8. ON THE VALIDITY OF (F5)

Before investigating how (F5) is valid, if at all, we must reconsider the

Peirce's notion of validity. Because he defined it in terms of truth-prod-

uctivity, there is no obvious format for validating inferences to appar-

ently non-truth-valued items such as recommendations, imperatives.

interrogatives, and the like. One might attempt to analyze (F5)-validity

by appeal to the truth-values of the performance propositions correlated

to the inferred recommendations, noting that propositions can be ques-

tioned, commanded or recommended (NEM 4:248). Yet, this approach

affords little hope; the conclusions of valid ampliative inferences can

be false when their premises are true, and in particular, a recommen-

dation can be appropriate given the information supplied by the prem-

ises even though its corresponding performance proposition is not only

false but incapable of being inductively justified. How else might (F5)

be brought within the realm of valid inferences?

    A generalization upon the notion of truth-productivity is required,

and there are at least two ways to achieve it, neither of which require

the (F5)-conclusion to be truth-valued or dependent upon the truth of

a correlated proposition. The first generalizes the idea of productivity

by relying on a strict reading of Peirce's "justification" for abductive

inference. Thus, we cannot hope to attain rational explanations, reach

truth, or know anything of positive fact without abduction, that is,

unless we both generate hypotheses and select certain of them for

further testing (CP 2.777-786, 5.603, 5.17, 7.219). The reason (F5)-

inferences are valid is not that their conclusions are true if their premises

are -- the truth "produced" is never that of the conclusion's -- but

because accepting their conclusions is the only way we can uncover the

truth of any of the preferred hypotheses which happen to be true.

    There are two drawbacks of this approach, however. In the first

place, it leaves unanswered the question about what the semantic value

of the (F5)-conclusion itself is. While directives are not truth-valued,

presumably those that can be "validly" derived from true premises of

an (F5) sort differ in semantic status from the undesirable recommen-

dations of wnexplanatory or least economical hypotheses. Secondly, it

sacrifices a uniform account of abductive validity. Abductive thinking

extends beyond the search for plausible explanatory theories, indeed,

every decision represents a hypothesis about what is best to do in

the circumstances (see Note 3). Insofar as such thinking is justifiable,

abductive inferences to directives having nothing to do with the search

for truth must be allowed, and there seems no way to construe their

validity in terms of truth production.

    The second interpretation restricts relevant production to the (F5)-

conclusion while preserving a uniform perspective on abductive cor-

rectness. It does so by generalizing upon the idea of truth, yet retaining

Peirce's formula that an inference is valid "if it possesses the sort of

strength that it professes and tends toward the establishment of the

conclusion in the way in which it pretends to do this" (CP 5.192). Thus,

a method can also be valid if it has the virtue of establishing conceptions

having a (semantic) value other than truth, viz., a question or recom-

mendation can be said to be legitimate or appropriate given the infor-

mation in the premises, and just as "P" follows necessarily from "P

is true," so a recommendation "R" follows necessarily from "R is

appropriate." A condition fixing appropriateness is as follows:
 

(L2)   A recommendation to further examine H is appropriate for

one who desires an explanation of C iff one is permitted (or, one ought),

so far as an explanation for C is desired, to examine H further.
 

That is, truth of a qualified normative necessarily determines the appro-

priateness of a corresponding directive and, consequently, supports the

directive itself. Considerations about which recommendation is appro-

priate all things being considered might yield a different judgment if

overriding normatives sanction a different recommendation; examining

H might be appropriate given certain ends but not other, even higher,

ends.15  Also, the workability of (L2) requires that there be some means

of determining when a normative is true and when one is overriding,

illustrating that a scrutiny of scientific methods cannot be separated

from normative and practical concerns. Peirce's teleological basis for

normative truth yields a rough, though flexible, formula for fixing nor-

mative truth and overridingness, and preserves the realist assumption

that whether H ought to be examined further is an objective matter

insofar as H advances the pursuit of truth. Retained is the distinction

among the three sorts of validity; deductive validity guarantees passage

from truth to a "preferred" semantic value, whether truth or appropri-

ateness, inductive validity yields the preferred value in the long run,

while abductive validity secures the preferred value if anything does.

    I am claiming that a uniform treatment of abductive reasoning re-

quires the broadened conception of validity characterized in this second

interpretation. But it carries a price. The very problem that plagued

(F3) resurfaces: why isn't (F5) deductively valid? If H is the most

plausible hypothesis, there can be no doubt but that one who desires

an explanation of C is permitted, qua investigator, to examine it further,

for the move from step (4) to (5) in (F5) seems an iron-clad guarantee of

securing the preferred semantic value of appropriateness. This follows

directly from (L2) and the normative component in Peirce's construal

of plausibility. Through their combined effect, (4) necessitates the claim

that the recommendation to further examine H is appropriate, and

from this, in turn, the recommendation itself necessarily follows. By

transitivity of the deductive linkage, therefore, the inference from (4)

to (5) is itself a matter of necessity. Since (5) just is the ultimate

conclusion of (F5), the latter is a deductively valid form.

    At this juncture, each of the claims A-E listed in Section I has been

defended. If the argumentation is cogent, then Peirce's writings provide

no grounds for the existence of an irreducibly third type of argument

correctness. This by no means denies the significance of his discussion

nor undermines the role of abductive reasoning in scientific inquiry.

The proper conclusion is that the value of Peirce's account does not

derive from the alleged autonomy of abduction, rather, from its empha-

sis upon the overtly practical phases of scientific reasoning.16
 
 

NOTES


1.  See CP 5.146 where the claim of irreducibility is made. Peirce denied that there was

any need to recognize a fourth category of reasoning. In 1911 he wrote,

I have constantly been on the alert for a fourth kind of reasoning, and have yet

never found the least vestige of any. . . I think myself entitled to presume, for the

present, that there is no such fourth form. (MS 856:6-9)

He stressed that argument by analogy is a mixture of the three elementary kinds (CF

2.733, 7.98) while other familiar types of argumentation, e.g., statistical deduction or

qualitative induction, are species of deduction and induction respectively.

All references to Peirce's writings are from the Collected Papersof Charles Sanders

Peirce, Harstshorne, C., Weiss, P., and Burks, A., (eds.), (Harvard University: Cam-

bridge, 1931-58): The New Elements of Mathematics, Eisele, C. (ed.), (Mouton: The

Hague, 1976); and the Houghton Library Peirce manuscripts numbered in accordance

with the R. Robin's Annotated Catalogue of thePapers of Charles S. Peirce (Massachu-

setts, 1967), with the page numbers being those of Ketner's. These are abbreviated,

respectively, by 'CP', 'NEM', and 'MS'.
 

2.  I will not address the claim that a logic of discovery is autonomous in that there is no

sharp distinction among the methods or reasons employed in selecting hypotheses foi

further test and those used in evaluating hypotheses (see Thagard 1981, and also Nickles

1985, p. 183, who attributes to Peirce this form of what he calls the "divorce thesis").

Moreover, the Peircean irreducibility thesis is distinct from variants of what Nickles calls

the "per se thesis," viz., that methods of generation per se are capable of conferring

justification upon a hypothesis in a way different from recognized deductive and inductive

procedures (Nickles 1985, p. 183). There is an interpretation of Peircean abduction that

does imply the per se thesis, namely, as a type of inference to the best explanation (see

Sections 3, 5 and 6). But this is not a correct interpretation of his mature view (Section

7), and if I am correct, abduction is not saddled with the controversy that surrounds

inference to the best explanation (Harman 1965, 1986, Boyd 1984, Van Fraassen 1989).

Nor is the irreducibility claim - that there are correct modes of abductive reasoning which

are neither deductively nor inductively valid - wedded to a construal of abduction as

inference to an explanatory hypothesis.

    Peirce emphasized that abductive validity has nothing to do with probability (CP

2.102), though, increasingly, he refused to characterize even inductive validity in terms

of probability (CP 2.781, 5.170; MS 293:20, 652:12), writing that induction "lends no

definite probability to its conclusion" (CP 2.780), and "does not render its conclusion

any more probable than it was before" (MS 475:8). By 1910 he labeled induction "verisim-

ilar" or "likely" reasoning while abduction was dubbed "plausible reasoning" (MS

652:13-16).
 

3.   Focus will be upon Peirce's post-1900 writings on abduction, for in 1898 he acknowl-

edged that he had previously confused abduction (also called 'hypothesis,' 'retroduction'

and 'presumption') with a species of probable inference (NEM 4:183 and see CP 2.102),

and in 1910 wrote,

. . . the division of the elementary kinds of reasoning into three heads was made by

me in my first lectures and was published in 1869 in Harris's Journalof Speculative

Philosophy. I still consider that it had a sound basis. Only in almost everything I

printed before the beginning of the this century I more or less mixed up Hypothesis

and Induction (CP 8.227).

In his later writings, Peirce is increasingly clear that abductive thinking extends beyond

the confines of scientific discovery, with "scientific retroduction" being but one species

of a generic type of reasoning (MS 637:5-6). Thus, we are constantly engaged in creative

thinking at some rudimentary level insofar as we seek solutions to problems, e.g.,

whenever we are thinking of what to do (Lieb 1988), what to say, or how to interpret

and describe what we observe (MS 692:27-8). We are continually searching for "action-

guiding" hypotheses in a manner similar to which the scientist is looking for explanatory

mechanisms to guide research, though under differing time constraints (MS 637:5).
 

4.  See also, CP 7.536, 2.444, 2.773, 4.53-5, 7.459, and MS L231:56). Every inference

involves an acceptance of a conclusion which, though caused by an acceptance of the

premises together with the reasoner's application of a general method or inference

pattern, is rule-governed. The rule, in turn, is reflected in a leadingprinciple of the

inference (CP 2.588-9) forming part of an agent's logica utens(CP 2.186, 5.108, 5.130).

or Peirce, a belief is a habit according to which one would act certain ways in given

circumstances, specifically, according to the expected logical consequences of the proposi-

tion believed. Moreover, a belief is described as a habit one is aware of, satisfied with,

does not struggle against, and which can be acquired merely by imagining situations and

the behavior they call for (MS 873:24-26). See CP 5.538-45 where the connection to

expectations is emphasized, and CP 1.645-6 where the relation to action is explicit. In

CP 5.538-9, Peirce distinguished practical from theoretical belief, then preceded to rank

the latter as a species of the former.
 

5.  See also CP 2.153, 5.191, 7.444, MS 692:5, MS 628:4. In places, Peirce distinguished

validity from strength (CP 5.192, 2.780) allowing that one argument can be stronger than

another though both are valid, e.g., an induction based on more instances, a deduction

with a more probable conclusion, or an abduction whose hypothesis has fewer competi-

tors. In CP 5.192, he defined validity in terms of strength, writing that an argument is

valid "if it possesses the sort of strength it professes and tends toward the establishment

of the conclusion in the way in which it pretends to do this." However, he did not define

strength, and in subsequent discussions the indicated measure of abductive strength is

built into the proper form of abductively selecting hypotheses for further pursuit (Sections

3 and 4).
 

6.   Peirce also argued that the three types of reasoning are differently justified, noting that

"we are always justified in presuming, for the purposes of conduct, that our sole end

may be reached" (MS L75:271 and compare MS 634:9-10), though here the emphasis is

not so much upon the method as upon use of the method. Justification for inferring by

way of a valid deductive method is justified because one is never led away from truth,

and use of a valid inductive method is justified because its conclusion "is reached by a

method which, steadily persisted in, must lead to true knowledge in the long run of cases

of its application" (CP 7.207, 2.725-40). Peirce offered at least three distinct yet related

justifications of abduction: (a) The human mind, having evolved under the influence of

natural laws, has a "natural tendency" (instinct) to think as nature is (MS 876:5). Man's

mind is attuned to the truth of things in order to discover what he has discovered (CP

6.476). (b) By sampling many abductions, we see that the results of reasoning abductively

are beneficial (MS 637:6-9, CP 2.270; 2.786), for humans would not have survived

without having knowledge and this requires abductive thinking (CP 5.603, NEM 4:320).

(c) Abduction is the only hope of attaining a rational explanation (CP 2.777, 5.145), of

regulating future conduct rationally (CP 2.270), of attaining our purposes of reaching

truth (CP 2.786) or of comprehending the universe (MS L75:272). Unless we reason

abductively we cannot know anything of positive fact (MS 475:43, CP 5.603, 5.171,

7.219). At one point Peirce argued that all justification rests on deduction, insofar as

abductive procedures can be justified inductively (CP 2.786) and inductive procedures

rest upon deduction (CP 5.170). This is no reduction of validity-types: it is the practice

of abductive reasoning that depends on inductive and deductive justifications, not the

validity of the forms.
 

7.  See CP 5.189-191. Conclusion indicators like 'hence', 'therefore', etc. must be under-

stood as having both a causal and normative force in depicting inferences, indicating not

only a transition from some acceptings (beliefs) to another, but that the speaker finds

the inference permissible. In displaying inference forms, however, they serve only the

latter function. See Harman 1986, pp. 1-10, for more on the distinction between reason-

ing and argument. (Fl) is the focus of concern in Hanson 1958, pp. 85-90, and has

tended to dominate the discussion of Peircean abduction ever since (though see Note 8

below). It is significant that by 1911, Peirce wrote; "I do not, at present, feel quite

convinced that any logical form can be assigned that will cover all 'Retroductions'. For

what I mean by a Retroduction is simply a conjecture which arises in the mind." (MS

L231:55).
 

8.  This fact undermines certain attempts to preserve (F2) as an originative mode of

inference. In considering a form similar to (F2), Peter Achinstein asks us to consider a

thought that one might have to the effect that a hypothesis H is plausible because H

provides an explanation given evidence and background information. It is possible, he

writes, that I have this thought without having been previously acquainted with H, hence,

that I first became acquainted with it in the course of making an inference to its plausibility

(Achinstein 1970, p. 98, and see Blachowicz 1989, pp. 450-1 who concurs with Ach-

instein). The latter clause is correct, but the former violates Peirce's vision that we are

reasoning to the plausibility of H from information about H, namely, that H not only

explains what we want explained, but is a more economical explanation than its competi-

tors. Hence, while it may be true to say that we first come to be acquainted with H "in

the course of making an inference" to H's plausibility, it does not follow that the

first acquaintance with H results from an inferential transition. Instead, the inference

presupposes our acceptance of various attributions to H..

    Addressing this issue, Douglas Anderson cautions against confusing "logical" with

"temporal" priority: while the conditional premise containing H is logically prior to the

conclusion, this does not mean that it is arrived at temporally prior to the conclusion,

for the premise and conclusion may be "simultaneously arrived at." Thus, Peirce's

canonical form in which the hypothesis already appears in the premises of abductive

inferences does not preclude the latter from being "insightful and originative" (Anderson

1986, p. 157). Anderson adds that "Peirce does not hold the ideas of insight and inference

to be mutually exclusive with respect to abduction," citing the fact that Peirce described

abduction as both instinctual and inferential within the span of a single lecture (p. 155).

The hypothesis is not arrived at independently of its explanatory role, but Anderson

overlooks Peirce's view that inference generates acceptance of the conclusion only if

there is a causal and temporal relation in the movement from premise to conclusion.
 

An inference is a passage from one belief to another: but not every such passage is

an inference... In inference one belief not only follows after another, but follows

from it. (CP 4.53, Peirce's emphasis)


The plausibility of claiming "simultaneous" awareness of premises and conclusion fades

even more dramatically when it is understood that a judgment of comparative economy

must itself be based upon a fairly extensive acquaintance with the hypothesis' merits (CP

7.218-232). Hence, if // occurs as an antecedent of a premise of an (F2)-inference, then

that inference cannot be the causal process that generated the first thought of H. The

more reasonable conjecture, therefore, is that (F2) is the canonical form for abductive-

preference, not discovery.
 

9.  In discussing his paradigm example of abduction, Kepler's discovery of elliptical orbits,

Peirce suggested that accepting the conditional premise is itself the product of inference

(CP 2.96,1.72-4).
 

10.  Not every case of belief causing belief is inference, even if it occurs by following a

rule (CP .53, MS 293:7-8), e.g., the inference-like "associational suggestions of belief."

See also CP 7.202, 2.776, and 5.171. In discussing the Associational psychologists Peirce

wrote:
 

The action by which, an association having once been established, that act by which

in accordance with it, one idea calls up another they called suggestion. I shall use

this terminology . . . (MS 318:38).
 

Suggestion is treated as a genus of which inference is only a species (CP 7.443, 1.606),

and it must be noted that he defined 'abduction' as the first adoption of a novel hypothesis

(CP 7.202, 6.525), not as the first conceiving of it. While every inference is tacitly rule-

governed, the agent's initial "irresistible" acceptance of it may be tempered by subsequent

evaluation of it by the norms of reasoning one accepts (CP 1.606) Thus, we can distinguish

among (i) initially conceiving that one might reason in a certain manner (the creative

observation), (ii) actually inferring in that manner (guessing), and (iii) evaluating the

reconstructed inference (cf., Achinstein 1980, p. 121 and Curd 1980, p. 203). I have also

discussed these issues in Kapitan 1990.
 

11.  Langley et al 1987, p. 14, classifies the heuristic procedures of hypothesis generation

as "inductive" sinre thev search for apnerfll theoriea frnm finitpdnt» thnncrh ir nninrs

out that Newton's derivation of the inverse square law of universal gravitation was a

deductive process that utilized an algebraic heuristic (pp. 54-7). Zahar 1983 champions

the deductivist approach to hypothesis discovery, viewing the theoretical innovations of

Maxwell's and Einstein's as well as that of Newton's as embodying deductive processes.

Pera 1980, 1987, on the other hand. finds the invention of hypotheses to be inductive,

though, equating inductive with ampliative, he does not view discovery in terms of

establishing an explanatory conditional. Inductive systems of discovery are also discussed

in Zytkow and Simon 1988. Achinstein 1980 distinguishes between rules codifying

heuristic strategies and inference rules in terms of generatingand justifying rules (p. 121).
 

12.  See Achinstein 1970, pp. 93-4 and Curd 1980, p. 214 for analogous forms. The notion

of plausibility has been variously interpreted. According to Thagard 1981, p. 249, Thomas

Goudge felt the conclusion of an abduction to be a statement of the form "it is plausible

to entertain H" with plausibility being a mode of acceptance (CP 8.222). Thagard,

however, finds plausibility to be a property of propositions, a reading more solidly

grounded in the texts CP 8.223, 2.662, 6.469-476 and MS 652:16.
 

13.  See Frankfurt 1958, p. 595 who similarly talks of "adopting" hypotheses inasmuch as

they are taken to deserve further consideration.
 

14.  This reading of Peirce goes against a common understanding of abduction as a type

of inference to the best explanation, but is closer to the interpretation offered in Hanson

1965, p. 64, and Curd 1980, p. 214, which take the abductive conclusion to be something

like (a). It is also analogous to the independent account of retroduction developed in

Achinstein 1987, which, nonetheless, shares the common understanding ofPeirce's view..

Achinstein claims that a "more guarded" claim, viz., that a theory Tis worth considering

further, is the sort of conclusion sanctioned by the mere explanatory success of 7" (pp.

423-5), and cites James Clerk Maxwell as a precursor of this view (p. 412). With the

conclusion of (F5), we move a step beyond the evaluative mode represented by (a) to

the more practical inference patterns culminating in directives, familiar in studies of

practical reasoning (see Castaneda 1975 and the papers in Raz 1978).
 

15.  A thorough discussion of the deductive character of practical reasoning and of the

rationale and grounds for assigning semantic values to imperatives, intentions and the

like, is offered in Castaneda 1975. His method of assigning semantic values to practical

directives is more complicated than what (L2) conveys, though it can be suitably adapted

to the reasoning involved in abductive-preference. I have expressed misgivings about his

explication of overridingness however (Kapitan 1984).
 

16.  The author is indebted to the National Endowment for the Humanities, the Southern

Regional Education Board, and East Carolina University for financial support, and to

Nathan Houser, Nicholas Georgalis, and Wolfgang Spohn for their helpful suggestions.
 
 
 
 
 
 
 

REFERENCES


Achinstein, Peter: 1970, 'Inference to Scientific Laws', MinnesotaStudies in Philosophyof Science 5,87-111.

Achinstein, Peter: 1980, 'Discovery and Rule Books', in Nickles 1980, pp. 117-137.

Achinstein, Peter: 1987, 'Scientific Discovery and Maxwell's Kinetic Theory', Philosophy of Science 54.409-434.

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