What does conjecture mean?
Conjecture refers to a judgment or belief formed when the available evidence is incomplete — in short, an educated guess. It functions both as a noun ('the report dismissed his theory as mere conjecture') and as a verb ('scientists conjecture that the species once roamed farther north'). Unlike a hypothesis, which is typically framed to be tested, conjecture often carries the implication of uncertainty and may even suggest idle speculation: calling something 'pure conjecture' is a way of saying it has no firm basis in fact. The word is at home in formal contexts — mathematics (where a conjecture is an unproven proposition awaiting demonstration), history, law, and science journalism — but it also serves everyday speech whenever we reason beyond what we actually know. Its Latin roots, literally 'throwing together', neatly capture its essence: piecing fragments into a plausible whole.
An opinion or conclusion formed on the basis of incomplete information; a guess or speculation.
"The ship's fate remains a matter of conjecture."
Often modified by adjectives emphasizing lack of evidence, as in 'pure conjecture' or 'idle conjecture'.
To form an opinion or supposition about something on the basis of incomplete evidence; to guess.
"Scholars conjecture that the text was written in the twelfth century."
Standard plural; used especially in academic and scientific writing when referring to multiple unproven propositions or speculations.
"Several of Euler's conjectures were later disproved by counterexample."
Every mathematical proof begins life as a conjecture — Fermat's famous 'last theorem' stayed one for over 350 years before anyone could prove it.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of conjecture
Conjecture derives from the Latin verb conicere, meaning 'to throw together', formed from com- ('together') and jacere ('to throw'). It entered English in the late Middle Ages via Old French, initially appearing in theological and scholarly use before broadening to mean any conclusion drawn from incomplete evidence. It shares the Latin root jacere with words such as project, reject, inject, and trajectory.
Related word forms
How conjecture is actually used
Register is neutral-to-formal; 'conjecture' appears often in academic, scientific, and journalistic writing where a more precise alternative to 'guess' is wanted. As a verb it takes a that-clause ('she conjectured that...') more often than a direct object. The adjective 'conjectural' is common in scholarly prose.
Easily confused with conjecture
Conjuncture means a combination of circumstances or a critical point in time, whereas conjecture means an unproven guess.