Abductive influence has aroused increasing interest and methodological discussion in various fields. In the philosophical context “abduction” or “retroduction” has, however, very often been subjected to severe criticisms as a logic of scientific discovery, especially that:

  • It is too weak a mode of inference to be of any use as it seems to permit inferences to all sorts of wild hypotheses; (Peter Achinstain, 1987); and
  • It cannot be a logic of discovery because the hypothesis is already included (or supposed to be known) in the premises (Hoffman, 1999, 278-9). By bringing in the Peircean ideas of “exploration”, “creativity”, categorization” and especially Paavola’s idea of “strategies”, I have argued in this paper that the classical counter – arguments against abduction are weak and not conclusive to exclude it from explanatory hypotheses in science.

The notion of “strategies” suggests, inter alia, that in abductive process, many inferential moves are taken into account simultaneously. Thus the concept of strategies is especially important in abductive reasoning. The thesis of this paper is that in the search for the logic of scientific discovery the focus should be more on methodological processes and not only on validity considerations which have dominated the discussion about abduction and thus have earned it much of the criticisms from some philosophers of science and other scholars.



Before C. S. Peirce, a great American philosopher, induction and deduction have been recognized as the only reasoning or logical processes that lead researchers to the truth or knowledge of reality. As a term expressing a reasoning process, “abduction” was first coined more than a hundred years ago by Peirce, to refer to an inference that involves the generation and evaluation of a hypothesis, i.e. a proposed explanation, for a phenomenon under investigation. Interest in the study of abductive inference had since declined, as it was also slow to develop, following logician’s concentration on deductive and inductive logic as the only logic we have.

In recent decades, however, there has been renewed interest in abduction, particularly, from two primary sources. First, philosophers of science have recognized its importance in the discovery and evaluation of scientific theories. Second, the researchers in artificial intelligence have realized that abduction is the key part of medical diagnosis and other tasks that require the exploration of or finding the best or most plausible explanatory hypothesis for a phenomenon. This explains Peirce’s description of it as a creative process, the result of which are subject to rational evaluation. Inspite of this, most logicians, scientists and philosophers of science have regarded abduction as a weak mode of inference compared to its rivals-induction and deduction, which appear and are applied in their works.

This paper makes a claim of contribution to the renewed interest, by contemporary philosophers of science in the debate on the epistemic status of abductive inference as a logic scientific discovery. The main project of this paper is to vindicate abductive inference as a logic and methodology of discovery in science involving exploration, categorization of the characters of the phenomenon under investigation and most especially “strategies” as methodological processes that lead to the knowledge of the appropriate hypothesis fit to be tested and used, for the explanation of the observed fact in nature.

The first part of this paper analyses the nature of abduction or retroduction in the Peircean logical system, in relation to other forms of logic – induction and deduction. The second part examines the basic criticisms against abduction as a logic of discovery. The third part focuses more on abduction as a methodology of discovery. Here the idea of “strategies” is projected as especially important in abductive reasoning. An important distinction made here is that between “definitory rules” of reasoning and “strategic rules” of reasoning. For the vindication of abduction as a logic of discovery, the paper submits that focus should be more on the methodological processes involved in it, rather than only on its validity based on its Peircean formulation.


Analysis of the Peircean Logical System

In his logical system Peirce ascribes important epistemic status and function for the logical processes of abduction, deduction and induction in the study, explanation and understanding of reality. In the same system of logic, as Tursman (1987) points out, Peirce views the knowledge of the world or reality as a progressive enterprise involving the three logical processes of abduction, deduction and induction (in that order). Understood from this perspective our knowledge of reality in general and of a phenomenon in particular, turns out to be a cooperative rather than a competitive enterprise of these three logical processes.

The Peircean logical system (Peirce, 1878b) presents abductive function as that of searching a pattern – a pathfinder as it were-in a phenomenon and suggesting a hypothesis. This means that abduction belongs to the informal sphere of logic which involves critical thinking, and hence different and distinct from deduction – formal sphere of logic consisting of the logic of symbolic forms (symbolic logic) – and induction. Thus although an abductive reasoning is usually illustrated with symbols for the sake of simplification, it remains a type of critical thinking which helps the researcher to “abduct” the most convincing, out of other convincing or plausible, alternative explanatory data analysis. The explanation is that there may be millions of possible explanations to a phenomenon, but considering the economy of research, the possibility of our falsifying every possibility becomes glaringly elusive. Moreover, from the epistemic standpoint it is not necessary to know everything in order to know something. By the same argument the researcher scientist does not have to screen every false thing in order to discover the authentic one. Peirce’s had something like this in mind when he contended, by way of analogy, that if animals have the instinct to do the right thing without struggling, we humans, too, as a specie of animal have the innate ability to make the right guesses and take right decisions intuitively. This is an assumption that may not easily be ignored.

What distinguish “abduction” or “retroduction” as an argument, for Aristotle, is that

… the relation of the middle to the last term is uncertain, though equally or more probably than the conclusion; or again an argument in which the terms intermediate between the last term and the middle are few. For in any of these cases it turns out that we approach more nearly to knowledge since we have taken a new term. (85).

The next implication is that the process of abduction does not amount to hasty judgement but judgement based on organized thought arising from proper categorization. This is to say that abduction does not lead to impulsive judgement; neither is it a matter of luck and chance nor is intuition a cheap source of knowledge. This presupposes that the application of exploratory data analysis (viewed in this paper as an integral aspect abduction) is no warrant for the analyst to be naïve to other researches related to the investigated phenomenon. The explanation is that abduction is a rigorous process, “the objective” of which, as Sullivan (1991) points out is “to determine which hypothesis or proposition to test, not which one to adopt or assert”. (27)

Thus, for Peirce according to Tursman (1987) “the progress of science depends on the observation of the right facts by minds furnished with appropriate ideas”. It is true that the intuitive judgement made by an intellectual is different from and more cogent than that made by a high school student. Peirce himself has cited several examples of remarkably correct guesses made by intellectuals, i.e. people whose minds have been furnished with appropriate ideas which in turn enable them to make correct judgements. Peirce’s list as cited by Tursman include:

  1. Bacon’s guess that heat was a mode of motion
  2. Young’s guess that the primary colours were violet green and red, and
  3. Dalton’s guess that there were chemical atoms before the invention of microscope (56).

The reliability of intuitive guesses such as these definitely presupposes and infact rests, as Peirce (1878b) pointed out in rational and proper categorization (in the Kantian sense) of the characters of the phenomenon under investigation. This analysis explains Peirce’s notion of knowledge as a continuous rather than a revolutionary process. Given this understanding, abductive process is not directed at the over-throw of previous paradigms, frameworks or categories, in the Kuhnian sense of “paradigm shift”; in short, abduction by intuition can be interpreted as observing the world with appropriate categories which arise from the internal structure of meanings rather than from experience. The implication of this, for researchers, is that the use of exploratory data analysis is neither exhaustive of all possibilities nor does it lead to hasty decisions in abductive process. Researchers must therefore be well equipped with proper categories into which the characters of a phenomenon may be placed in order to be able to seek out the invariant features and patterns of a phenomenon.

The two implications analysed and discussed above are subsumed in a third implication, namely, that the process of abduction is characteristically strategic. As the crux of this paper, a full discussion of this implication is reserved for the next section of this paper.

Deduction also is accorded a status in Peircean logical system. After suggesting a plausible hypothesis, the next stage according to Peirce (1878b) is to refine the hypothesis with logical deduction. Deduction is drawing logical consequences from premises. The conclusion is true given that the premises are true also; and the argument is valid or invalid depending on whether or not the conclusion is derived logically from the premises. For instance:

All As are Bs

C is B

Therefore, C is A.

This process of reasoning for Peirce, is self-referent and cannot lead to progress in knowledge, since knowing is an activity which by definition, is an involvement with the real world. Moreover, for Peirce, deduction along is a necessary condition, but not a sufficient condition of knowledge.

Induction introduced by Fancis Bacon many years ago into scientific thinking and investigation is a direct opposite of deduction. It is logic based upon the ideas that probability is the relative frequency in the long run and that a general law can be arrived at based on observation of numerous cases. For example,

A1, A2, A3……A100 are B

A1, A2, A3….. A100 are C

Therefore, B is C.

David Hume (1777/1912) had argued that the results of a logical process such as this are inconclusive because in infinite time there are always new cases and new evidence. Moreover, for Hume, induction belongs to the province of “matters of fact”; and “for every matters of fact”, according to Hume “the contrary is always possible.”

But induction was also accorded some consideration in Pericean logical system. For Peirce (1878b) (as later accepted by Rudolf Carnap), induction is a self-corrective system. Peirce’s problem with induction is that “induction cannot furnish us with new ideas because observations or sensory data lead to superficial conclusions but not to the bottom of things (878). Nevertheless Peirce believes that induction still has validity in that given a large number of cases, we can approximate the actual probability. In effect we do not according to Forster (1993) have to know everything in order to know something. Also we do not have to know every cases in order to get an approximation. This approximation, in Peirce’s view, is sufficient for a researcher to fix his beliefs and to make further inquiries in order to arrive at a goal.

Peirce’s intention, I suppose, was to bring out the differences in the merits and shortcomings of both deduction and induction. Both logical processes cannot generate new hypothesis; only abductive logic can. He speaks of induction as the experimental testing of a finished theory. He says induction

…sets out with a theory and measures the degree of concordance of that theory with fact, it never can originate any idea whatever. No more can deduction. All the ideas of science come to it by the way of abduction. Abduction consists in studying facts and devicing a theory to explain them. Its only justification is that if we are ever to understand things at all, it must be in that way. Abductive and inductive reasoning are utterly irreducible, either to the other or to Deduction, or Deduction either of them… (146).

Thus for Peirce a reasoner and researcher should apply abduction (first), deduction (second) and induction (third) altogether in order to achieve a comprehensive inquiry. At the abductive stage of inquiry, the investigator’s goal is to explore the data concerning a phenomenon under investigation, find out a pattern, and suggest a plausible hypothesis by proper categorization of the properties of that phenomenon. Thereafter, deduction is brought in to build a logical and testable hypothesis based upon other plausible premises, and finally, induction is brought in by way of making approximation towards the truth in order to fix his beliefs for further inquiry about that phenomenon. In short for Peirce, scientific inquiry/discovery rests in three major logically cooperative processes namely, creative, explicatory and verificatory processes which are provided by abduction, deduction and induction. The basic claim of this paper, is that discovery in science is possible majorly because the abductive process that brings about the discovery is characteristically strategic (or goal directed). We will come back to the analysis and discussion of the latter claim, after examining the basic criticisms against abduction as a logic of discovery in science.


The Basic Criticisms against Abduction as a Logic of Scientific Discovery

Abductive inference in the philosophical, scientific and various other fields has aroused increasing interest and methodological discussion but has also been subjected, especially in the philosophical context, to serious classical counter arguments especially when presented as a logic of discovery. These arguments have been centered exclusively on the validity of abductive inference. The basic criticisms include:

  • That abduction is too weak a mode of inference to be of any use and
  • That in its basic formulation, hypothesis is already presupposed to be known, and that this is not the way hypotheses are discovered in the first place.

These counter arguments rest on the widely held view that discovery is something that cannot be treated by conceptual or philosophical means. And this arises from the basic way in which Peirce (1867) himself, as we said earlier, formulated abduction:

The surprising fact, C, is observed 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 (189).

A simple way of restating Peirce’s formulation is this:

The surprising phenomenon is observed among hypotheses A,B, and C; A is capable of explaining X. hence, there is a reason to pursue A.

The implication of this argument is that abduction can be interpreted as a mode of inference by which one can search for an explanation for a certain surprising (or anomalous) phenomenon. But an inference such as this in Paavola’s view (267-283) can be criticized because it is too permissive to be of any use, in that it seems to permit inference to all sorts of wild hypotheses. Peter Achinstein (413), too, has presented some often cited counter – examples in line with this criticism. First the hypothesis that “I will be paid a million dollars if this paper is published”, would explain (if it were true) why I am writing this paper. Yet I have no justification to infer from this that I am about to be become a millionaire.

Again, Achinstein (409) argues, suppose that I am happy about some news I have just received. A hypothesis would be suggested that I have won the noble price in philosophy because it is reasonable to suppose that anyone who hears the news about the noble price wining is happy. But again, the fact that I am happy should give no reasons or warrant to believe that I have won the Nobel Prize. So, he concludes, from the mere fact that a certain hypothesis H, (granting that it is true) would explain a certain fact, it does not necessarily follow that there is a reason to think that, the hypothesis in view is true (410). But an important thing to note about this counter-argument is that, although it appears to be appealing, it fails to take into account that the fact observed should somehow be “surprising”.

Hoffmann (278-9), too, rejects abduction as a logic of discovery. His argument is that the suggested explanatory hypothesis itself, by Peirce’s account, is already a part of the premises. Thus, it seems that the new idea is not a product of abductive inference and is even traceable to something different. The logic is that given this analysis and understanding, abduction could rather be, at most, passed as a logic fit for the preliminary appraisal of a hypothesis that has already been discovered by some other means. In this sense, too, abduction turns out to be that phase of activity to be carried out after the discovery itself had been made, but before it has actually been justified (confirmed or refuted). But taking this position presupposes that the old distinction, which Reichenback tried to make between the context of discovery and the context of justification, is inadequate, not even necessary in scientific thinking. Moreover, the criticisms that we have considered could be given much attention only if one limits the concept of the logic of discovery to the mastery of the “definitory” rules of logic (or reasoning). If we go beyond this by taking also into account the “strategic” rules of reasoning, abduction could be adequately defended as a more promising candidate for a logic of discovery in many fields of studies especially in scientific field.

The strong contention here is that the critics’ clutches could be escaped if emphasis is layed more on the distinction between “definitory” rules and “strategic” rules and in the application of the latter in reasoning concerning an observed phenomenon. Jaakko Hintikka had observed 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… students are not taught  how to reason well but to maintain their logical virtue (35).

There is some truth in Hintinkka’s observation. Many of us, the teahers of logic, not only in Nigerian Universities, today are caught-up by this serious omission. Many recommended introductory logic textbooks for beginners and even for their teachers concentrate on how the students can avoid committing logical fallacies, and learn what is, and what is not admissible and valid. In order to achieve this goal we tend to focus our students’ mind on learning those rules that tell them what are the valid rules in a particular system of logic, understood as “definitory” rules. By doing so the study of the “strategic” rules, as it is applied in the game of chess, for instance, suffers a total neglect.

The glaring consequence, by way of analogy, is that a person who knows only the definitory rules of the game of chess cannot claim to be excellent in chess game as excellence in chess game requires that a person should master the strategic rules well; the same idea applies for logic. Thus no student can be excellent in logic and reasoning by merely knowing only the definitory rules; excellence is attainable only by mastering well the strategic rules in logic. The preoccupation of the next section of this paper, therefore, is the analysis of the notion of strategy and the method of strategizing as integral and very important aspect of abductive reasoning involved in the search for explanatory hypothesis leading to new discovery concerning a phenomenon.


The Method of Strategizing as an Integral Aspect of Abductive Reasoning in Science

It is true that “strategies” is a neglected topic in philosophy of science but an important claim, which is made in this section, is that abductive inference as a logic and methodology of scientific discovery can be defended by an appeal to strategic principle and method rather than to validity based on application of definitory move-by-move rules. The concept of strategy although complicated is generally related to a teleological or goal-directed search, activity or process, where the ability or skill to anticipate things, appraise and choose between different possibilities or alternatives are crucial. Thus the central idea about strategic rules is that such rules cannot normally be assessed partially in terms of detached or unconnected moves or steps, but in terms of the entire network of the whole strategic situation.

This means that in strategizing, many but interconnected steps can and must be taken into account simultaneously. This paper, however, does not claim by this characterization to have exhausted the meaning of “strategies” in relation to abductive inference, rather it is stressing an essential point, namely that the consideration of “validity” alone is inadequate in the appraisal of the status of abductive logic and reasoning process of scientific discovery. And it could be conjectured that the need to emphasize strategizing as abductive and a promising route to discovery is suggestive of the need to erase the erroneous assumption that abduction is a weak mode of inference. Sami Paavola’s suggestion seems to give credence to this conjecture when he said:

The force of abductive inference is much strengthened if one takes into account the hypotheses are to be searched for in relationship to various phenomenon and not just in order to explain one, surprising phenomena (56).

The point, which Paavola seems to make here is that  a researcher who is looking for a good explanatory hypothesis for a certain anomalous phenomenon should ensure that his explanation accounts for, or atleast be consistent with most other clues and information available to him concerning the subject matter. The supposition is that such hypothesis has some chance of survival in subsequent tests and assessment. Following the actual practice of science, too, the researcher should also, ensure that the proposed explanation hypothesis is not totaling unconvincing; or if it seems to be so, then he should look for a better explanation. This is part of the “freedom” of science.

These then seem to be strategic principles according to which more than one move can be, and should be taken at the same time. Simply put therefore, it may be said that a strategically good hypothesis takes into account that there is an explanation for one’s initial explanation, or at least, explanation why there cannot be any further explanation. In order words a strategic process involves taking relevant background information into account and providing further evidence for some odd hypothesis in order to prove its mettle, i.e. show why it should be dropped in the process. The explanation is that in strategies or strategic reasoning associated with the process of discovery, the reasoned attempts to anticipate the relevant background information as well as provide further evidence for odd hypothesis. This process of reasoning automatically rules out the possibility of what the critics had referred to as “wild hypothesis”.

Given this analysis analysis and understanding the notions of “strategic reasoning” can be said to have a sort of logical and epistemic affinity with the notion of “discovery”. “Discovery” connotes the idea that something new is brought or “abducted” to a particular situation. But strategies must be taken into account when surprising or “aha-experiences’ or intuitive insights are involved. The explanation is that the surprising experience becomes significant only when the hypothesis in question fits with, and takes account of all the information, hints, clues, constraints and moves that are involved in the entire problem situation. In this case the strategic researcher is not limited to the explanation of some detached anomalous phenomenon but would be able to take into account, at the same time, the counter arguments, all available information, steps or moves and then choose among other alternatives the hypothesis that results to scientific discovery.

Many discoveries in science had been arrived at through this means. For instance, the idea of evolution and the Malthusian principle for Darwin, were important discoveries only because these ideas could be extended to accommodate larger arguments concerning species, and not as separate and unrelated explanations. This process of outlining taking notes of constraints, hints and inferential moves, we contend are akin to strategic thinking, at least in the sense “strategies” is used in our discussion. Thus a good insight is also a good one strategically.

Strategies are also involved, I suppose, when it is said that  abductive reasoning starts from anomalous or somewhat surprising phenomenon. But it is not certain whether the emphasis which some philosophers lay on this really affects the validity of this reasoning, irrespective of whether it starts from surprising or non-surprising phenomenon. But this, too, can be judged as a strategic rule. The explanation is that, in difficult problems, or in cases where something new is required, it is a good strategy to start from surprising facts or from little details and try with them to find a solution or a hypothesis.

It is, therefore, difficult to accept the critics’ rejection of abduction as a logic of discovery on the ground that the hypothesis or idea is already presupposed in the premises (which amounts to a violation of definitory rule). In the first place, this paper does not claim that abductive inference is an automatic means of making discovery. It claims rather that if abduction is to be a logic of discovery, the whole methodological processes must be taken into account; i.e. the investigator must not only concentrate on the validity of Peirce’s basic formulation of abductive argument. It is important, for example, for the investigator to think of how the “surprising fact” operates as a clue in search for an explanatory hypothesis. The difficult part in abductive search, from the point of view of the investigator, might be to find fruitful premises. But this does not warrant the conclusion that abduction cannot analyse properly the logical form of discoveries.

So the way this paper interprets the idea of abductive search, from the strategic point of view is that a hypothesis suggested can in itself be something old and even well known. But the way in which this hypothesis squares with the problem or fact under investigation and, at the same time, with other relevant clues to that problem is crucial in any discovery. It is also essential that there is a further clarification for the hypothesis. For example, the idea of evolution, which was mentioned earlier, was not new when Charles Darwin proposed it. It was widely admitted as a good explanation for various phenomena that there was no plausible explanation for how evolution operates, most especially as there seemed to be the problem was lots of evidence which were against the evolutionary hypothesis itself.

The point we are typing to make here is that the basic formula for abductive inference can be an essential part in the logic of discovery even though the hypothesis is in the premises, granting that the difficult part in discovery is the recognition that the hypothesis really is a viable way of solving a particular problem, and that the hypothesis works more generally and not only in relationship to one particular anomalous phenomena.

The implication here is that in order to understand the importance of abductive reasoning in scientific discovery, the investigator’s interest should be more on methodological processes. And by laying emphasis on application of strategies it is implied, too, that inquiry should be understood as a kind of problem-solving process, where the inquirer uses the best inquiry strategies possible. The application of strategies therefore explains why the inquiry cannot be said to be purely blind, even when something new is discovered. This is so because the inquirer is required to take into account, as pointed out earlier, all available information and clues that are relevant to the subject matter. Strategically, therefore, and form the point of view of the inquirer, it would amount to bad reasoning to suggest a wild hypothesis based purely on chance. In order to avoid this it become more reasonable for the researcher to take into account existing knowledge. This amounts to nothing over and above critical thinking.

What this means is that the investigator should be able to combine the new ideas with existing knowledge constraints, or be able to show that the existing knowledge is in some ways inadequate. The said constraints may be negative in terms of inhibiting new ideas; they may be positive in terms of suggesting methods, theories which should be taken into account, and which might provide information and clues on how to solve the problem in question.

This idea is similar to the role of “normal science” or “paradigms” in Thomas Kuhn’s famous model of scientific growth (1970). From the strategic point of view too, this methodological process is supported by Hanson’s basic idea concerning the logic of discovery. Citing Handson, Paavola, for instance states that:

It is a reasoning, which proceeds retroductively, from an anomaly to the delineation of a kind of explanatory h, which fits, into an organized pattern of concept (280).

This unveils, too, the strategies aspects of abduction, which involves taking into account the constraints, and hints that help in hypothesis finding. Thus the goal in abductive inference at east, in most cases is to find an overall pattern into which all relevant evidence and clues fit; i.e. it is a method of inquiry which requires that the various constraints and clues be taken into account and the various inferential moves be put together successfully by the researcher.



Logicians and philosophers of science in recent times have turned their concentration from analyzing the structure of finished product to the actual process of inquiry. These processes were literally defined as something that can neither be analyzed by conceptual means nor by philosophical modes. But as Guttman (2004) points out, with the distinction made between “heuristic” appraisal and “epistemic” appraisal in methodology, emphasis has been shifted to the conceptual means of reaching out for the process of inquiry and discovery, especially when rationality of discovery is searched for.

Moreover, it is the feeling of most philosophers of science, like Hintikka (1998) and Aliseda (2001) that there is need for the expansion of the concept of rationality, if the context of discovery is to be taken into account. This paper sees a fresh opportunity for this expansion by developing a means of arriving at the processes of inquiry and discovery.

Thus, this paper has attempted to show the possibility of developing a new and more appropriate formal model and tool for these processes. Thus the logical apparatus should be broadened since the traditional deductive and inductive logic for this matter becomes rather inadequate, while the deductive model is especially needed in order to understand the process of discovery.

This necessitates the inquirer not only to concentrate on the validity of abductive inference upon which the whole interest of the critics rest but to take also into account the importance of strategies in abduction as a logic and methodology of discovery especially in the study of science. Thus this paper makes a distinction between definitory rules and strategic rules. With this distinction emphasis in this paper is on the importance of strategies in abductive process in the search for explanatory hypothesis.

The Peircean logical system describes abduction as an exploratory and creative process. In this paper we have argued that abductive inference is also characteristically strategical (or goal-directed) in terms of taking altogether into account the existing knowledge, constraints, hints, information, clues and inferential moves that help the searcher in finding an appropriate hypothesis for the explanation of a phenomenon. Thus, these processes exploratory, categorization, creative and strategical – are subsumed in the notion of abduction. Abduction, therefore, does not amount to a mere trying out anything or hasty judgement but observing a phenomenon with appropriate categories strategically.

The critics’ challenges against abduction on the basis of their interpretation of the Peircean formulation breakdown, especially as their interpretation has not taken into account the important distinction that this paper has made between “definitory rules” and “strategic rules” in logic and reasoning. By this distinction and the attendant emphasis on the application of strategic rules of reasoning the researcher will avoid the mistake of limiting the concept of the logic of discovery to the mastery of the definitory rules of logic and to go beyond this by viewing discovery in terms also of the application of strategic reasoning. Given, this wider conceptions and focus more on methodological processes, abduction is defensible both as a logic and methodology of scientific discovery.



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