Editing Abductive reasoning (section)

====Overview====
The American philosopher Charles Sanders Peirce introduced abduction into modern logic. Over the years he called such inference ''hypothesis'', ''abduction'', ''presumption'', and ''retroduction''. He considered it a topic in logic as a normative field in philosophy, not in purely formal or mathematical logic, and eventually as a topic also in economics of research.

As two stages of the development, extension, etc., of a hypothesis in scientific [[inquiry]], abduction and also [[inductive reasoning|induction]] are often collapsed into one overarching concept—the hypothesis. That is why, in the [[scientific method]] known from [[Galileo Galilei|Galileo]] and [[Francis Bacon|Bacon]], the abductive stage of hypothesis formation is conceptualized simply as induction. Thus, in the twentieth century this collapse was reinforced by [[Karl Popper]]'s explication of the [[hypothetico-deductive model]], where the hypothesis is considered to be just "a guess"<ref>{{cite book|last=Popper|first=Karl|title=Conjectures and Refutations: The Growth of Scientific Knowledge|location=London|publisher=Routledge|edition=2|date=2002|page=536}}</ref> (in the spirit of Peirce). However, when the formation of a hypothesis is considered the result of a process it becomes clear that this "guess" has already been tried and made more robust in thought as a necessary stage of its acquiring the status of hypothesis. Indeed, many abductions are rejected or heavily modified by subsequent abductions before they ever reach this stage.

Before 1900, Peirce treated abduction as the use of a known rule to explain an observation. For instance: it is a known rule that, if it rains, grass gets wet; so, to explain the fact that the grass on this lawn is wet, one ''abduces'' that it has rained. Abduction can lead to false conclusions if other rules that might explain the observation are not taken into account{{mdash}}e.g. the grass could be wet from [[dew]]. This remains the common use of the term "abduction" in the [[social science]]s and in [[artificial intelligence]].

Peirce consistently characterized it as the kind of inference that originates a hypothesis by concluding in an explanation, though an unassured one, for some very curious or surprising (anomalous) observation stated in a premise. As early as 1865 he wrote that all conceptions of cause and force are reached through hypothetical inference; in the 1900s he wrote that all explanatory content of theories is reached through abduction. In other respects Peirce revised his view of abduction over the years.<ref>See Santaella, Lucia (1997) "The Development of Peirce's Three Types of Reasoning: Abduction, Deduction, and Induction", 6th Congress of the [[IASS]]. [http://www.pucsp.br/~lbraga/epap_peir1.htm Eprint].</ref>

In later years his view came to be:
* Abduction is guessing.<ref name="guess">Peirce, C. S. 
* "On the Logic of drawing History from Ancient Documents especially from Testimonies" (1901), ''Collected Papers'' v. 7, paragraph 219.
* "PAP" ["Prolegomena to an Apology for Pragmatism"], MS 293 c. 1906, ''New Elements of Mathematics'' v. 4, pp. 319–320.
* A Letter to F. A. Woods (1913), ''Collected Papers'' v. 8, paragraphs 385–388.
(See under "[http://www.helsinki.fi/science/commens/terms/abduction.html Abduction]" and "[http://www.helsinki.fi/science/commens/terms/retroduction.html Retroduction]" at ''Commens Dictionary of Peirce's Terms''.)</ref> It is "very little hampered" by rules of logic.<ref name="HL">Peirce, C. S. (1903), Harvard lectures on pragmatism, ''Collected Papers'' v. 5, [http://www.textlog.de/7664-2.html paragraphs 188–189].</ref> Even a well-prepared mind's individual guesses are more frequently wrong than right.<ref>Peirce, C. S. (1908), "[[s:A Neglected Argument for the Reality of God|A Neglected Argument for the Reality of God]]", ''Hibbert Journal'' v. 7, pp. 90–112, see §4. In ''Collected Papers'' v. 6, see paragraph 476. In ''The Essential Peirce'' v. 2, see p. 444.</ref> But the success of our guesses far exceeds that of random luck and seems born of attunement to nature by instinct<ref name="NA">Peirce, C. S. (1908), "[[s:A Neglected Argument for the Reality of God|A Neglected Argument for the Reality of God]]", ''Hibbert Journal'' v. 7, pp. 90–112. See both part III and part IV. Reprinted, including originally unpublished portion, in ''Collected Papers'' v. 6, paragraphs 452–85, ''Essential Peirce'' v. 2, pp. 434–50, and elsewhere.</ref> (some speak of [[logical intuition|intuition]] in such contexts<ref>Peirce used the term "intuition" not in the sense of an instinctive or anyway half-conscious inference as people often do currently. Instead he used "intuition" usually in the sense of a cognition devoid of logical determination by [[a priori and a posteriori|previous cognitions]]. He said, "We have no power of Intuition" in that sense. See his "Some Consequences of Four Incapacities" (1868), [http://www.peirce.org/writings/p27.html Eprint] {{Webarchive|url=https://web.archive.org/web/20110514094121/http://www.peirce.org/writings/p27.html |date=2011-05-14 }}.</ref>).
* Abduction guesses a new or outside idea so as to account in a plausible, instinctive, economical way for a surprising or very complicated phenomenon. That is its proximate aim.<ref name="NA" />
* Its longer aim is to economize [[inquiry]] itself. Its rationale is inductive: it works often enough, is the only source of new ideas, and has no substitute in expediting the discovery of new truths.<ref>For a relevant discussion of Peirce and the aims of abductive inference, see McKaughan, Daniel J. (2008), "[https://muse.jhu.edu/article/252833/summary From Ugly Duckling to Swan: C. S. Peirce, Abduction, and the Pursuit of Scientific Theories]", ''Transactions of the Charles S. Peirce Society'', v. 44, no. 3 (summer), 446–468.</ref> Its rationale especially involves its role in coordination with other modes of inference in inquiry. It is inference to explanatory hypotheses for selection of those best worth trying.
* [[Pragmatism]] is the logic of abduction. Upon the generation of an explanation (which he came to regard as instinctively guided), the [[pragmatic maxim]] gives the necessary and sufficient logical rule to abduction in general. The hypothesis, being insecure, needs to have conceivable<ref>Peirce means "conceivable" very broadly. See ''Collected Papers'' v. 5, paragraph 196, or ''Essential Peirce'' v. 2, p. 235, "Pragmatism as the Logic of Abduction" (Lecture VII of the 1903 Harvard lectures on pragmatism): {{blockquote|It allows any flight of imagination, provided this imagination ultimately alights upon a possible practical effect; and thus many hypotheses may seem at first glance to be excluded by the pragmatical maxim that are not really so excluded.}}</ref> implications for informed practice, so as to be testable<ref name="L75">Peirce, C. S., Carnegie Application (L75, 1902, ''New Elements of Mathematics'' v. 4, pp. 37–38. See under "[http://www.helsinki.fi/science/commens/terms/abduction.html Abduction]" at the ''Commens Dictionary of Peirce's Terms'': {{blockquote|Methodeutic has a special interest in Abduction, or the inference which starts a scientific hypothesis. For it is not sufficient that a hypothesis should be a justifiable one. Any hypothesis which explains the facts is justified critically. But among justifiable hypotheses we have to select that one which is suitable for being tested by experiment.}}</ref><ref name="prag">Peirce, "Pragmatism as the Logic of Abduction" (Lecture VII of the 1903 Harvard lectures on pragmatism), see parts III and IV. Published in part in ''Collected Papers'' v. 5, paragraphs 180–212 (see 196–200, [http://www.textlog.de/7663.html Eprint] and in full in ''Essential Peirce'' v. 2, pp. 226–241 (see sections III and IV). {{blockquote|.... What is good abduction? What should an explanatory hypothesis be to be worthy to rank as a hypothesis? Of course, it must explain the facts. But what other conditions ought it to fulfill to be good? .... Any hypothesis, therefore, may be admissible, in the absence of any special reasons to the contrary, provided it be capable of experimental verification, and only insofar as it is capable of such verification. This is approximately the doctrine of pragmatism.}}</ref> and, through its trials, to expedite and economize inquiry. The economy of research is what calls for abduction and governs its art.<ref name="econ">Peirce, C.S. (1902), application to the Carnegie Institution, see MS L75.329-330, from [http://www.cspeirce.com/menu/library/bycsp/l75/ver1/l75v1-08.htm#m27 Draft D] {{Webarchive|url=https://web.archive.org/web/20110524021101/http://www.cspeirce.com/menu/library/bycsp/l75/ver1/l75v1-08.htm#m27 |date=2011-05-24 }} of Memoir 27:
{{blockquote|Consequently, to discover is simply to expedite an event that would occur sooner or later, if we had not troubled ourselves to make the discovery. Consequently, the art of discovery is purely a question of economics. The economics of research is, so far as logic is concerned, the leading doctrine with reference to the art of discovery. Consequently, the conduct of abduction, which is chiefly a question of [[heuristic]] and is the first question of heuristic, is to be governed by economical considerations.}}</ref>

Writing in 1910, Peirce admits that "in almost everything I printed before the beginning of this century I more or less mixed up hypothesis and induction" and he traces the confusion of these two types of reasoning to logicians' too "narrow and formalistic a conception of inference, as necessarily having formulated judgments from its premises."<ref>Peirce, A Letter to [[Paul Carus]] circa 1910, ''Collected Papers'' v. 8, paragraphs 227–228. See under "[http://www.helsinki.fi/science/commens/terms/hypothesis.html Hypothesis]" at the ''Commens Dictionary of Peirce's Terms''.</ref>

He started out in the 1860s treating hypothetical inference in a number of ways which he eventually peeled away as inessential or, in some cases, mistaken:
* as inferring the occurrence of a character (a characteristic) from the observed combined occurrence of multiple characters which its occurrence would necessarily involve;<ref name="NCA">(1867), "On the Natural Classification of Arguments", ''Proceedings of the American Academy of Arts and Sciences'' v. 7, pp. 261–287. Presented April 9, 1867. See especially starting at [{{google books |plainurl=y |id=nG8UAAAAYAAJ|page=284}} p. 284] in Part III §1. Reprinted in ''Collected Papers v. 2, paragraphs 461–516 and ''Writings'' v. 2, pp. 23–49.''</ref> for example, if any occurrence of ''A'' is known to necessitate occurrence of ''B, C, D, E'', then the observation of ''B, C, D, E'' suggests by way of explanation the occurrence of ''A''. (But by 1878 he no longer regarded such multiplicity as common to all hypothetical inference.<ref name="DIH">Peirce, C. S. (1878), "Deduction, Induction, and Hypothesis", ''Popular Science Monthly'', v. 13, pp. 470–82, see [{{google books |plainurl=y |id=u8sWAQAAIAAJ|page=472}} 472]. ''Collected Papers'' 2.619–44, see 623.</ref>[https://en.wikisource.org/wiki/Popular_Science_Monthly/Volume_13/August_1878/Illustrations_of_the_Logic_of_Science_VI Wikisource])
* as aiming for a more or less probable hypothesis (in 1867 and 1883 but not in 1878; anyway by 1900 the justification is not probability but the lack of alternatives to guessing and the fact that guessing is fruitful;<ref name="L2L">A letter to Langley, 1900, published in ''Historical Perspectives on Peirce's Logic of Science''. See excerpts under "[http://www.helsinki.fi/science/commens/terms/abduction.html Abduction]" at the ''Commens Dictionary of Peirce's Terms''.</ref> by 1903 he speaks of the "likely" in the sense of nearing the truth in an "indefinite sense";<ref>"A Syllabus of Certain Topics of Logic'" (1903 manuscript), ''Essential Peirce'' v. 2, see p. 287. See under "[http://www.helsinki.fi/science/commens/terms/abduction.html Abduction]" at the ''Commens Dictionary of Peirce's Terms''.</ref> by 1908 he discusses ''plausibility'' as instinctive appeal.<ref name="NA" />) In a paper dated by editors as ''circa'' 1901, he discusses "instinct" and "naturalness", along with the kind of considerations (low cost of testing, logical caution, breadth, and incomplexity) that he later calls methodeutical.<ref>Peirce, C. S., "On the Logic of Drawing History from Ancient Documents", dated as ''circa'' 1901 both by the editors of ''Collected Papers'' (see CP v. 7, bk 2, ch. 3, footnote 1) and by those of the ''Essential Peirce'' (EP) ([http://www.iupui.edu/~peirce/ep/ep2/headers/ep2headx.htm#8 Eprint] {{Webarchive|url=https://web.archive.org/web/20120905022758/http://www.iupui.edu/~peirce/ep/ep2/headers/ep2headx.htm#8 |date=2012-09-05 }}. The article's discussion of abduction is in CP v. 7, paragraphs 218–31 and in EP v. 2, pp. 107–14.</ref>
* as induction from characters (but as early as 1900 he characterized abduction as guessing<ref name="L2L" />)
* as citing a known rule in a premise rather than hypothesizing a rule in the conclusion (but by 1903 he allowed either approach<ref name="HL" /><ref name="newidea">Peirce, C. S., "A Syllabus of Certain Topics of Logic" (1903), ''Essential Peirce'' v. 2, p. 287:
{{blockquote| The mind seeks to bring the facts, as modified by the new discovery, into order; that is, to form a general conception embracing them. In some cases, it does this by an act of ''generalization''. In other cases, no new law is suggested, but only a peculiar state of facts that will "explain" the surprising phenomenon; and a law already known is recognized as applicable to the suggested hypothesis, so that the phenomenon, under that assumption, would not be surprising, but quite likely, or even would be a necessary result. This synthesis suggesting a new conception or hypothesis, is the Abduction.}}</ref>)
* as basically a transformation of a deductive categorical syllogism<ref name="DIH" /> (but in 1903 he offered a variation on ''modus ponens'' instead,<ref name="HL" /> and by 1911 he was unconvinced that any one form covers all hypothetical inference<ref name="kehler">A Letter to J. H. Kehler (1911), ''New Elements of Mathematics'' v. 3, pp. 203–4, see under "[http://www.helsinki.fi/science/commens/terms/retroduction.html Retroduction]" at ''Commens Dictionary of Peirce's Terms''.</ref>).