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# Conjecture

A conjecture is a proposition that is unproven but is thought to be true and has not been disproven. Karl Popper pioneered the use of the term "conjecture" in scientific philosophy. Conjecture is contrasted by hypothesis (hence theory, axiom, principle), which is a testable statement based on accepted grounds. In mathematics, a conjecture is an unproven proposition or theorem that appears correct.

## Famous conjectures

The Langlands program is a far-reaching web of these ideas of 'unifying conjectures' that link different subfields of mathematics, e.g. number theory and representation theory of Lie groups; some of these conjectures have since been proved.

## Counterexamples

Formal mathematics is based on provable truth. In mathematics, any number of cases supporting a conjecture, no matter how large, is insufficient for establishing the conjecture's veracity, since a single counterexample would immediately bring down the conjecture. Conjectures disproven through counterexample are sometimes referred to as false conjectures (cf. Pólya conjecture).

Mathematical journals sometimes publish the minor results of research teams having extended a given search farther than previously done. For instance, the Collatz conjecture, which concerns whether or not certain sequences of integers terminate, has been tested for all integers up to 1.2 × 1012 (over a million millions). In practice, however, it is extremely rare for this type of work to yield a counterexample and such efforts are generally regarded[by whom?] as mere displays of computing power, rather than meaningful contributions to formal mathematics.

## Use of conjectures in conditional proofs

Sometimes a conjecture is called a hypothesis when it is used frequently and repeatedly as an assumption in proofs of other results. For example, the Riemann hypothesis is a conjecture from number theory that (amongst other things) makes predictions about the distribution of prime numbers. Few number theorists doubt that the Riemann hypothesis is true (it is said that Atle Selberg was once a sceptic, and J. E. Littlewood always was). In anticipation of its eventual proof, some have proceeded to develop further proofs which are contingent on the truth of this conjecture. These are called conditional proofs: the conjectures assumed appear in the hypotheses of the theorem, for the time being.

These "proofs", however, would fall apart if it turned out that the hypothesis was false, so there is considerable interest in verifying the truth or falsity of conjectures of this type.

## Undecidable conjectures

Not every conjecture ends up being proven true or false. The continuum hypothesis, which tries to ascertain the relative cardinality of certain infinite sets, was eventually shown to be undecidable (or independent) from the generally accepted set of axioms of set theory. It is therefore possible to adopt this statement, or its negation, as a new axiom in a consistent manner (much as we can take Euclid's parallel postulate as either true or false).

In this case, if a proof uses this statement, researchers will often look for a new proof that doesn't require the hypothesis (in the same way that it is desirable that statements in Euclidean geometry be proved using only the axioms of neutral geometry, i.e. no parallel postulate.) The one major exception to this in practice is the axiom of choice—unless studying this axiom in particular, the majority of researchers do not usually worry whether a result requires the axiom of choice.

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• conjecture — [ kɔ̃ʒɛktyr ] n. f. • 1246; lat. conjectura 1 ♦ Opinion fondée sur des probabilités ou des apparences. ⇒ hypothèse, supposition. Parler de qqch. par conjecture. Conjecture sur l avenir. ⇒ prévision, pronostic. 2 ♦ (Nuance péj.) Opinion fondée sur …   Encyclopédie Universelle

• conjecture — CONJECTURE. s. f. Jugement probable, opinion que l on fonde sur quelques apparences touchant quelque chose obscure & incertaine. Forte, foible, puissante conjecture. legere, vaine conjecture. conjecture trompeuse. conjecture bien fondée, mal… …   Dictionnaire de l'Académie française

• conjecture — CONJECTURE. subs. fém. Jugement probable, opinion que l on fonde sur quelques apparences touchant une chose obscure et incertaine. Forte conjecture. Puissante conjecture. Foible, légère, vaine conjecture. Conjecture trompeuse, bien fondée, mal… …   Dictionnaire de l'Académie Française 1798

• conjecture — vb Conjecture, surmise, guess are comparable as verbs, meaning to draw an inference from slight evi dence, and as nouns, denoting an inference based upon such evidence. Conjecture implies formation of an opinion or judgment upon what is… …   New Dictionary of Synonyms

• conjecture — Conjecture, Coniectura, Coniectatio. Faulse conjecture, Fallax coniectura. Entendre par conjecture, Coniectura consequi. Qu on scait par conjectures, Coniecturalis. Choses desquelles on peut faire quelque conjecture, Res positae in coniectura. On …   Thresor de la langue françoyse

• conjecture — I noun assumption, belief, guess, guesswork, hypothesis, imputation, inference, opinion, postulate, postulation, presumption, presupposition, presurmise, speculation, supposal, supposition, surmise, suspicion, theory, thesis, unverified… …   Law dictionary

• conjecture — [kən jek′chər] n. [ME < L conjectura, a putting together, guess, inference < conjectus, pp. of conjicere, to throw together, guess < com , together + jacere, to throw: see JET1] 1. an inferring, theorizing, or predicting from incomplete… …   English World dictionary

• Conjecture — Con*jec ture, v. t. [imp. & p. p. {Conjectured}; p. pr. & vb. n. {Conjecturing}.] [Cf. F. conjecturer. Cf. {Conject}.] To arrive at by conjecture; to infer on slight evidence; to surmise; to guess; to form, at random, opinions concerning. [1913… …   The Collaborative International Dictionary of English

• Conjecture — Con*jec ture (; 135?), n. [L. conjectura, fr. conjicere, conjectum, to throw together, infer, conjecture; con + jacere to throw: cf. F. conjecturer. See {Jet} a shooting forth.] An opinion, or judgment, formed on defective or presumptive… …   The Collaborative International Dictionary of English

• conjecture — late 14c., interpretation of signs and omens, from O.Fr. conjecture surmise, guess, or directly from L. coniectura conclusion, interpretation, guess, inference, lit. a casting together (of facts, etc.), from coniectus, pp. of conicere to throw… …   Etymology dictionary

• conjecture — [n] speculation, assumption conclusion, fancy, guess, guesstimate*, guesswork, hunch, hypothesis, inference, notion, opinion, perhaps, presumption, shot in the dark*, sneaking suspicion, stab in the dark*, supposition, surmise, theorizing,… …   New thesaurus