Virtual Centre for Peirce Studies at the University of Helsinki


ABDUCTION AS A LOGIC AND METHODOLOGY OF DISCOVERY:
THE IMPORTANCE OF STRATEGIES

Paper originally published in (2004) Foundations of Science 9(3), 267-283. Published on the Commens site with the kind permission of the editors of the journal.

Sami Paavola
University of Helsinki
E-mail: sami.paavola at helsinki.fi


Abstract: There are various "classical" arguments against abduction as a logic of discovery, especially that 1) abduction is too weak a mode of inference to be of any use, and 2) in basic formulation of abduction the hypothesis is already presupposed to be known, so it is not the way hypotheses are discovered in the first place. In this paper I argue, by bringing forth the idea of strategies, that these counter-arguments are weaker than may appear. The concept of strategies suggests, inter alia, that many inferential moves are taken into account at the same time. This is especially important in abductive reasoning, which is basically a very weak mode of inference. The importance of strategic thinking can already be seen in Charles S. Peirce´s early treatments of the topic, and N. R. Hanson´s later writings on abduction although they did not use the concept of "strategies." On the whole, I am arguing that the focus should be more on methodological processes, and not only on validity considerations, which have dominated the discussion about abduction.
Key words: abduction, logic of discovery, strategies, methodology


1. Basic Criticism against Abduction (as a Logic of Discovery)

Abductive inference arouses increasing interest and methodological discussion in various fields. In the philosophical context abduction has, however, very often been subjected to severe criticism (see e.g., Frankfurt, 1958; Nickles, 1980b; Kapitan, 1992). There are, so to speak, various "classical" counter-arguments against abduction, especially if abduction is presented as a logic of discovery. A basis for these counter-arguments is the widely held view that discovery is something that cannot be treated by conceptual or philosophical means.
One basic way of formulating abduction is the one made already by Charles S. Peirce (See Peirce, CP 5.189; Hanson, 1972, 86):

The surprising fact, C, is observed;             {268}
  But if H [an explanatory hypothesis] were true, C would be a matter of course,
  Hence, there is reason to suspect that H is true.

So abduction can be understood as a mode of inference where explanations are searched for (anomalous or suprising) phenomena. But this kind of an inference can be criticized because it is too permissive to be of much use. It seems to permit inferences to all sorts of wild hypotheses (Frankfurt, 1958, 596; Nickles, 1980a, 24; Kapitan, 1992, 6). Peter Achinstein has presented various, often cited, counter-examples in line with this criticism. For example, the hypothesis that I will be paid one million dollars if this paper is published, would explain (if it were true) why I am writing this paper. But still, there is no reason to think that I am about to come a millionaire (unfortunately so!). Or another Achinstein example: Let us suppose as an observed fact that I am happy about some news I have just received. Then a hypothesis could be proposed that I have just received the news that I have won the Nobel Prize in literature (because it is reasonable to suppose that anyone who hears the news about the Nobel Prize winning is happy). But here again, the fact that I am happy, should give no reason to believe that I have won the Nobel Prize. So, from the mere fact that some hypothesis H, if it was true, would explain the data, does not usually follow that there is reason to think that that H is true (Achinstein, 1970, 92; 1971, 118; 1987, 413). It is to be noted that Achinstein does not take into account that the fact observed should somehow be 'surprising' (Is it surprising that I am writing this paper? Is it surprising that I am happy? In what sense are these facts supposed to be surprising?). But still, Achinstein's argument appears to be basically adequate. The problem with abduction is that its basic formula seems to allow these kinds of inferences to all sorts of wild and crazy hypotheses.
Another basic criticism against abduction is that it cannot be a logic of discovery because the hypothesis is already included (or supposed to be known) in the premises (see above the second premise) (e.g., Frankfurt, 1958, 594; Nickles, 1980a, 23; Hoffmann, 1999, 278-9). So it seems that the new idea is not a result of abductive inference, and abduction can be at most a logic for preliminary evaluation or appraisal of a hypothesis that {269} is already discovered by some other means (Schon, 1959, 501-2; Kapitan, 1992, 2). In this sense abduction is often placed in that phase of activity which is carried out after original discovery but before final justification (e.g., Nickles, 1980a, 18-22; Laudan, 1980, 174). This means -- if the idea is followed -- that the old distinction between the context of discovery and the context of justification (see Reichenbach, 1938; Nickles, 1980a) is not enough, and a third region is needed. The basic idea is that this third area can be analysed by logical and conceptual means, although it is not a matter of justification in proper sense yet. But the context of discovery in genuine sense is still, according to this idea, something inexplicable, or possibly a subject for empirical sciences but not for conceptual analysis.


2. The Meaning of Strategies in Abduction

I think that abduction can still be defended as a very promising candidate for a logic of discovery if the meaning of strategies is taken into account. Jaakko Hintikka has emphasized a distinction between two sorts of rules in reasoning and logic (or in games in general): the definitory rules and the strategic rules. Hintikka maintains that for the theory of logic and reasoning, especially at the level of introductory textbooks and courses, the study of excellence of reasoning is often forgotten, and the emphasis is on the avoidance of mistakes in reasoning (e.g., Hintikka, 1999). According to him, students are not taught how to reason well but to maintain their logical virtue (i.e., to avoid logical fallacies and to learn what is and what is not admissible and valid). The focus has been on definitory rules of logic, and strategic rules have largely been neglected. The definitory rules tell what are valid rules in particular system of logic. By analogy: the definitory rules of chess tell what one is allowed to do in chess (how chessmen may be moved etc.). But by knowing only the definitory rules of chess one cannot say that one plays chess well. Excellence in chess requires that one master strategic rules extremely well. According to Hintikka, this same idea applies to logic. No one is good in logic and reasoning by knowing only the definitory rules of logic, but by mastering well the strategic rules.
Strategies have, however, been a quite neglected topic in philosophy of science. There are some exceptions. In the interrogative {270} approach to inquiry, the meaning of strategies has been emphasized (Hintikka, 1985, 1989; Jung, 1996). But usually the merits of inference are assessed by investigating whether the truth of the premises guarantees or makes probable the truth of the conclusion. And this has also been the basic way of evaluating abduction.
Hintikka has emphasized strategic aspects also in relationship to abductive inference: "the validity of an abductive inference is to be judged by strategic principles rather than by definitory (move-by-move) rules" (Hintikka, 1998, 513). Hintikka himself does not, however, treat abduction as a separate mode of inference in his interrogative model of inquiry. In Hintikka's model the problem of abduction is subsumed under a more general problem concerning the nature of ampliative reasoning in general. In Hintikka's model, abduction is closely related to a question- answer step in the process of inquiry (ibid., 519-523).
I suggest that abduction as a separate mode of inference can also be defended by taking strategies into account much more seriously than before (see also Magnani, 1999, 235- 236). But what does strategies mean in the area of reasoning? Strategy is in itself a very complicated concept. Strategies are related to goal-directed activity, where the ability to anticipate things, and to assess or choose between different possibilities, are important (see e.g., Hintikka, 1989, 1999). One central point in strategic rules is that they cannot normally be judged only in relationship to particular moves, but the whole strategic situation must be taken into account (see Hintikka, 1998, 513). This means that in strategies more than one step or move can and must be taken into account at the same time. I am not maintaining that this characterization does full justice to the meaning of strategies in (abductive) inference, but it is surely one essential point. And in abduction, strategies are especially important because it is basically such a weak mode of inference. The force of abductive inference is much strengthened if one takes into account that the hypotheses are to be searched for in relationship to various phenomena and background information and not just in order to explain one, surprising phenomenon.
So if I am a researcher looking for a good explanatory hypothesis for some anomalous phenomenon, I can (and must) try to constrain and guide my search by taking into account that my explanation {271} must explain or at least be consistent with, most other clues and information that I have available concerning the subject matter. And I try to anticipate that my explanation has some chance of survival in subsequent tests and assessments. Usually I must also take into account that the proposed explanation should not be totally unconvincing, or if it seems to be that, I should have a good further explanation for why this explanation still deserves attention. So, I should have an explanation for my explanation (see Thagard & Shelley, 1997). These are strategic principles where more than one move can and should be taken into account simultaneously.
In Achinstein's counterexamples, one important reason why those wild hypotheses are not reasonable (it is to be noted that the term "reasonable" is just the right one here) is that they do not fit well with other relevant information. Normally no one would pay one million dollars for any academic paper (unfortunately again!), which rules out this hypothesis as strategically bad. And there is no reason to think that I have won the Nobel Prize in literature - only because I am happy - if this hypothesis does not fit at all with other information concerning who I am and what I have done. Strategically, it would be bad reasoning to suggest such implausible hypotheses, if there were no good further reasons or backing for these. A strategically good hypothesis takes also into account that there is an explanation for my explanation (or at least explanation why there cannot be any further explanation). Why someone would pay me one million dollars for this paper? Why would someone even suggest a Nobel Prize for me? If there are no good answers for these questions, there is no point in even suggesting these kinds of hypotheses at the first place. Achinstein himself apparently notices the situation: normally we take the relevant background information into account, and we require further evidence for some odd hypothesis in order to take it seriously (see Achinstein 1970, 92; 1971, 118; 1987, 416). But what Achinstein is missing is the idea that strategies are involved here.
The strategic viewpoint does not, however, rule out the possibility of suggesting implausible hypotheses altogether. It is, for example, possible to imagine such a course of events, where the one million dollars hypothesis (or the Nobel Prize hypothesis) is the correct one, because of some extraordinary circumstances. Especially if {272} more conventional or plausible hypotheses have not worked out, it might be a good strategy to try more implausible hypotheses. (In Achinstein's one-million dollars example, if the situation were that, for some reasons, it would be very surprising that I am giving this presentation, and other explanations would not seem to work out, it would be a good candidate hypothesis to think that someone is paying me a lot of money for this.) What I am arguing is that in strategies, the reasoner tries to anticipate the counter-arguments, and to take into account all the relevant information, and this rules out very "wild" hypotheses, except, when there is no other available, or alternatively, when these are presented simply as "wild guesses".
I will now give further consideration to the criticism that abduction cannot be the logic of discovery because the hypothesis or the idea is already presupposed in the premises. To begin with, I am not maintaining that abductive inference is an automatic means for making discoveries. I agree with N. R. Hanson, who emphasized that abductive inference is rather a way of analysing conceptual issues in discoveries rather than "a manual" or an algorithmic device for making these discoveries (Hanson, 1961, 21-22). If abduction is to be considered as the logic of discovery, the whole methodological process must be taken into account; one must not just concentrate on the form of the argument. In this sense, it is for example important to think how these "surprising facts" (see the formulation of abduction above) operate as clues in the search for explanations or hypotheses. From the point of view of the inquirer, the difficult part in abductive search might be to find fruitful premises. But this does not mean that abduction cannot analyse properly the logical form of discoveries.
Strategies are also involved here. Although the hypothesis is in the premises, abduction can still be the logic of discovery because, as Peirce wrote (Peirce, CP 5.181):

"It is true that the different elements of the hypothesis were in our minds before; but it is the idea of putting together what we had never before dreamed of putting together which flashes the new suggestion before our contemplation."

How I interpret this idea from the strategic viewpoint is that a hypothesis suggested can in itself be something old and even well known. But the way in which this hypothesis is seen to fit with this particular problem in question {273} and with other relevant information (besides the one anomalous phenomenon) is crucial. And it is also essential that there is a further explanation or clarification for this particular hypothesis. For example, the idea of evolution was not new when Charles Darwin proposed it. It was widely admitted that it would have been a good explanation for various phenomena, but the problem was that there were no plausible explanations for how evolution operates more specifically (and in fact there seemed to be lots of evidence which was against the evolutionary hypothesis). As Darwin later recollected his discovery and its relationship to the known facts (Darwin in his autobiography: Barlow, 1958, 118-119):

"It was evident that such facts as these [various important observations that he had made on the famous voyage of the Beagle], as well as many others, could be explained on the supposition that species gradually become modified; and the subject haunted me. But it was equally evident that neither the action of the surrounding conditions, nor the will of the organisms (especially in the case of plants), could account for the innumerable cases in which organisms of every kind are beautifully adapted to their habits of life. I had always been much struck by such adaptations, and until these could be explained it seemed to me almost useless to endeavour to prove by indirect evidence that species have been modified."

And likewise many details in Darwin's theory were not new, but the real discovery and insight was that Darwin showed that these ideas really work in this particular context. This is also how Howard Gruber has described Darwin's famous Malthusian insight (Gruber, 1981, 42):

"… his notebooks show that he had or almost had the same idea a number of times before, during the fifteen months of deliberate effort leading up to the moment in question. So the historic moment was in a sense a re-cognition of what he already knew or almost knew."

So my point is, that the basic formula of abduction can still be an essential part in the logic of discovery (even though the hypothesis is in the premises) if the difficult part in discovery is the recognition that the hypothesis really is a viable way of solving this particular problem and that the hypothesis works more generally (and not only in relationship to one, particular anomalous phenomenon).
I am not maintaining that the importance of strategies in discovery means that in (scientific) discovery the researchers always {274} have their hypotheses already at their disposal and that the only problem would be to strategically see, somehow, a connection between moves in games of reasoning. Discovery means that something new is brought (or abducted!) to the particular situation. But strategies must be taken into account when "aha-experiences" or insights are involved. An aha-experience means that the hypothesis (or the solution) in question fits with those constraints and clues that are involved in the problem situation in question, i.e., the insight seems to take into account many counter-arguments and moves in advance. It is not enough that the hypothesis explains only some detached, anomalous phenomena (e.g., for Darwin the idea of evolution and the Malthusian principle were important discoveries only when these ideas could be integrated to the larger argument concerning species, and not as separate and unconnected explanations). It almost seems that the basis for the aha-experience is a situation where, first, various constraints and hints characterize the situation and then some solution seems to fit with these constraints. And this outlining of constraints and hints is, I submit, closely related to strategic thinking, at least in the sense I use 'strategies' here. A good insight is also a good one strategically.
I think that strategies are also involved when it is said that abductive inference starts from anomalous or somewhat surprising phenomena. It might be asked, why it is so often emphasized that abductive inference starts from surprising phenomena (but cf. Hoffmann, 1999, 281)? It does not seem to affect to the validity of inference if it starts from surprising or from non-surprising phenomenon. I think that this is also a strategic rule, for the following reasons: In difficult problems or in cases where something new is required, it is a good strategy (or a worthwhile one) to start from anomalous facts or from little details, and try with them to find a solution or a hypothesis. This is at least a strategy that detectives (or detective novels) recommend (the connection between abduction and the reasoning that detectives use is often noticed, see e.g., Eco & Sebeok, 1988; Niiniluoto, 1999b). This is also how Francis Darwin described how (his father) Charles Darwin worked (Darwin, 1892, 94-95):

"There was one quality of mind which seemed to be of special and extreme advantage in leading him to make discoveries. It was the power of never letting {275} exceptions pass unnoticed. Everybody notices a fact as an exception when it is striking or frequent, but he had a special instinct for arresting an exception. A point apparently slight and unconnected with his present work is passed over by many a man almost unconsciously with some half-considered explanation, which is in fact no explanation. It was just these things that he seized on to make a start from."


3. Strategies in Peirce's and Hanson's Treatment of Abduction: Methodeutic for Abduction

Charles Peirce's seminal writings concerning abduction already contained many strategic insights, although he did not label them as such (Hintikka, 1998, 512- 6). Peirce made a distinction between three areas of logic: (Speculative) Grammar, Critic, and Methodeutic. Peirce characterized this "trivium" in various ways during his long career, so it is not possible to interpret this distinction in exact terms or unequivocally (see e. g., Peirce, CP 1.559; CP 1.444; CP 2.93). Especially the third area, Methodeutic, leaves room for various interpretations (in many writings he called it e.g., "Speculative Rhetoric") (Liszka, 1996). In Grammar the nature and meanings of signs are studied; in Critic arguments are classified and the validity and the force of arguments are studied (see Peirce, CP 1.191). Methodeutic, however, "studies the methods that ought to be pursued in the investigation, in the exposition, and in the application of truth." (ibid.), and "the principles of the production of valuable courses of research and exposition." (Peirce, EP2, 272).
In order to develop further the model of abductive inference, all these three Peircean areas of logic (Grammar, Critic, Methodeutic) are salient. According to Peirce, Critic is important in abduction although it is a very "weak" mode of inference (Peirce, CP 5.188):

"… abduction, although it is very little hampered by logical rules, nevertheless is logical inference, asserting its conclusion only problematically or conjecturally, it is true, but nevertheless having a perfectly definite logical form."

The area of Grammar should also be developed further in order to better understand the nature of abductive inference. For example, the special role of iconic and perceptual elements in abductive inference is, I think, part of Grammar (see Peirce, CP, 2.96; Shelley, 1996; Thagard and Shelley, 1997). But what is important from the {276} point of view of this paper is that, in abductive inference, the role of Methodeutic can be seen as especially significant because, in Peirce's words, "Of the different classes of arguments, abductions are the only ones in which after they have been admitted to be just, it still remains to inquire whether they are advantageous." (Peirce, HP, 1035)
I maintain that according to the Peircean distinction of these three areas of logic, strategies would belong to Methodeutic. Methodeutic studies the process of inquiry and the way in which inquiry is carried on, and strategies are part of it. As Peirce in his time emphasized Methodeutic in reasoning, Hintikka, in recent decades has emphasized the need for strategic rules and study of fruitful methods of logical reasoning.
There are also other concepts and ideas in Peirce´s writings (besides Methodeutic) where the issue of strategies comes to the fore. Hintikka has suggested that in Peirce's concept of habit "there lurks … a strategic rule trying to get out" (Hintikka, 1998, 515). Peirce also emphasized the notion of "the economy of research," which is very closely related to strategic principles (Peirce, CP 7.220). According to Peirce various sorts of "economical" (broadly interpreted) factors should guide the choice of the hypotheses, for example, caution, which takes into account what will happen if the hypothesis suggested does not work out. One example of this economical caution is the game of twenty questions where the idea is to guess what object someone is thinking by making good questions (ibid.). Only such questions are allowed as can be answered by Yes or No (this limitation makes the game intriguing; there would be no game if you were allowed to ask the object thought of right away). The success in this game is based on skilful questions that break up the search area most efficiently. I think it is quite clear that this is the same as saying that the success is based on good strategies.
Peirce himself often maintained that we humans must have some sort of an instinct that guides our guesses (see e.g., Peirce, CP 2.753; CP 5.172-4). Peirce's argument was that a human could not arrive at his or her theories by pure chance. There are an infinite number of theories that could be suggested if there is nothing that helps us. According to Peirce our abductive guesses are not totally {277} haphazard or blind because we have an instinct for making these guesses. But this explanation raises several questions. Is there any evidence that we humans have this kind of a guessing instinct? How would it operate? There is some plausibility to the Peircean idea that evolution has moulded us to guess such hypotheses about physical and psychical life, which have been important for our survival. But how could this guessing instinct help humans to discover modern scientific theories which are often counter-intuitive and against a common sense way of understanding things? Peirce himself admitted that this instinct explanation is not very plausible when one considers the genesis of very complicated theories by which we "penetrate further and further from the surface of nature" (Peirce, CP 7.508; see also Peirce, CP 7.606). It is also problematic to combine this instinct explanation with the idea that abduction is a third mode of inference. It seems that if the crucial element in abduction is the guessing instinct there is not much room for abductive reasoning. There are various suggestions how instinct and inference can be combined in a Peircean scheme (e.g., Fann, 1970; Anderson, 1987) but still it is a quite problematic how this combining could satisfactorily be done.
Nicholas Rescher has suggested that Peirce's "somewhat mysterious" capacity of instinct should be replaced by a methodology of inquiry (Rescher, 1995, 321-3; Hoffmann, 1999, 297). The idea is that scientific inquiry and discovery is not blind because methods and methodology give rational principles that guide the processes of inquiry. Methods themselves, according to Rescher, have emerged through evolutionary trial-and-error process. I am not trying to evaluate Rescher's solution comprehensively, but I think that Rescher is making a very important point here. Scientists need not start from scratch because methods and methodologies that have proven to be successful are guiding inquiry. But it seems that Rescher's solution cannot be the whole story. If methods and methodology are supposedly reached by trial-and-error, are we not facing again the same problem that was supposed to be solved (this is one version of the classical Meno paradox)? Are these methods found by pure chance in evolutionary way? Is this possible? And if so, is there some kind of an agreement what these successful methods nowadays are? If they guide scientific inquiry in contrast {278} to instincts, should we not know them explicitly? And even if we could characterize these methodologies in general terms, is there any guarantee that they work in particular cases?
What I have tried to argue has some similarities to Rescher's solution. There is no need to abandon the idea that we humans might have some abilities that can be called "instincts" and which help us when we are trying to discover something new. But these abductive instincts cannot be the fundamental basis for abductive inference. In order to understand abductive reasoning better, the focus should be more on methodological processes. But unlike Rescher, I don't think that the most important feature of methodology is that it is moulded by evolutionary process.
The focus on strategies means that inquiry is seen as a kind of a problem solving process where the inquirer uses the best inquiry strategies possible. The use of strategies explains why inquiry is not purely blind, even when something new is discovered. The inquirer must try to take into account all the information that is relevant to his or her subject area. Strategically, and from the point of view of the inquirer, it would be bad reasoning to suggest very "wild" hypotheses, or hypotheses based on pure chance; it is wise to take into account existing knowledge. It is true that new (especially revolutionary) discoveries often mean that some parts of this existing knowledge must be abandoned. But even then the inquirer must be able to combine the new ideas with existing knowledge or constraints, (or to be able to show that the existing knowledge is in some ways inadequate). These constraints can be negative, in a sense that they inhibit new ideas, but they can also be positive in suggesting methods, theories, information and so on which must be taken into account and which might give clues how to solve the problems in question. This idea is similar to the role of "normal science" or "paradigms" in Thomas Kuhn´s famous model of scientific growth (Kuhn, 1970). Paradigms are not automatic ways of solving problems, but they give good suggestions for how to conduct inquiry. This is the reason why inquiry does not always have to start from scratch. Kuhn does not extend the idea to revolutionary situations where paradigms themselves change. But even in revolutionary situations, existing knowledge constrains and guides the search for new information and discoveries. {279}
I think that Norwood Russell Hanson´s old ideas concerning abduction should also be seen from a strategic angle. Hanson was already a proponent of the idea of the logic of discovery in the 1950s and 1960s when these subjects were not popular in philosophy of science (Hanson, 1961, 1972). Hanson's formulations have been criticized as inadequate for the logic of discovery (see e.g., Nickles, 1980b). My suggestion is that this criticism has been concerned more with the validity of abduction (with "Critic" in Peircean terms), and Hanson himself was more interested in abduction as a part of methodological processes of inquiry (i.e., Methodeutic). Hanson explicitly criticized the "logic of the finished research reports;" he put the emphasis on processes of discovery and maintained that these processes can be analysed by conceptual means (Hanson, 1961, 20- 22).
In his writings concerning abduction, Hanson distinguished three ingredients in "the logic of discovery" (Hanson, 1965, 47-65). It is reasoning which

"1) proceeds retroductively, from an anomaly to
  2) the delineation of a kind of explanatory H which
  3) fits into an organized pattern of concepts." (ibid., 50)

I think that these points can be seen as strategic principles although Hanson himself did not develop these ideas explicitly in this way. The starting point in anomalies (point 1) can be seen as a strategic principle (see the end of chapter 2. above). Hanson also pointed out that abduction does not mean that some particular hypothesis is found straight away. An important phase in the process of discovery might be that the type of the solution is delineated before the solution is acquired (point 2) (Hanson, 1961; Niiniluoto, 1999a, S440-1). This is strategic thinking: the constraints and hints that help in hypothesis finding are taken into account. And the goal in abductive inference (at least in most cases) is to find an overall pattern into which all evidence and clues fit (point 3), and this phase especially requires that various inferential moves be put together skilfully and by taking various clues and constraints into account (a paradigmatic case is detective stories, but this is in itself a very general model). {280}


4. Conclusion: A Logic and Methodology of Discovery

Various approaches in the philosophy of science nowadays emphasize the need to find a model for inquiry that is not strictly logical, at least in the "old" sense (i.e., in the sense that formal logic has been usually understood in the last century) but one that is not purely relativistic or historicistic either (see e.g., Pera, 1994; Jung, 1996; Thagard, 2000; Aliseda, 2001). This need arises especially from an aim to understand processes of discovery and knowledge formation and not just finished products (Sintonen, 1996; Aliseda 1997). Philosophy of science and logic have for long concentrated on analysing the structure of finished products, e.g., what is an explanation, and not processes of inquiry, e.g., how good explanations are searched for and found (Aliseda, 2001). There have been some notable exceptions, e.g., N. R. Hanson, but usually these processes were literally defined to be something that cannot be analysed by conceptual means, or by philosophical models.
Thomas Nickles has made a distinction between "heuristic appraisal" and "epistemic appraisal" in methodology (Nickles, 1989). Epistemic appraisal is the standard way of doing things in the philosophy of science. It is a retrospective, justificatory assessment of scientific results. Heuristic appraisal means that the promisingness, or fertility of scientific proposals or problems is being assessed. It can be maintained that this is at least as important, if not more important than epistemic appraisal. Nowadays heuristical aspects are often emphasized when rationality of discovery is searched for (Jung, 1996; Magnani, 1999, 235-236; Aliseda, 2001).
The "friends of discovery" have for long emphasized that the concept of rationality must be broadened if the context of discovery is to be taken into account (Nickles, 1980b). There is a new opportunity for this broadening when new conceptual means are developed, i.e., conceptual means that try to capture processes of inquiry and discovery (see e.g., Hintikka, 1985, 1998; Sintonen, 1996; Jung, 1996; Aliseda, 1997, 2001). The basic point is that even though old models of formal and symbolic logic are not adequate, it is possible to develop new formal models and tools that are more appropriate for this (see also Thagard, 2000). In this sense there is no need to leave "the context of discovery" only to psychologists {281} or to empirical scientists, for there are also conceptual and logical issues involved here.
The point in this paper has been that the logical apparatus should be broadened at least in two dimensions from the "standard" way. Deductive logic is not enough, and the model of abductive inference is especially needed in order to understand the processes of discovery. But abduction in itself is not enough. Besides validity considerations (which are in themselves important in abduction) there is the art of using (abductive) reasoning. This concerns the area of "Methodeutic" (in Peircean terms); an area especially important in abductive reasoning. It seems that this is in some sense a return to a pre-Fregean sense of logic, where the boundaries between logic and methodology are quite vague (Aliseda, 2001); boundaries between logic and psychology must also be drawn anew (see Thagard, 2000). In any case, this shift to focus more on processes of inquiry necessitates a re-consideration of abductive strategies.


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