ὑπόθεσις

Hypothesis comes from Greek ὑπόθεσις (hypóthesis), a compound of ὑπό (hypó, 'under, below') and θέσις (thésis, 'a placing, a proposition'), from τιθέναι (tithénai, 'to place, to set'). The literal meaning is 'a placing under' — the foundational assumption or supposition upon which an argument or narrative rests. In ancient rhetoric and literary theory, a hypothesis was the particular case or plot that a more general argument or work was built on: the hypothesis of a tragedy was its specific dramatic scenario, the particular story placed underneath the general patterns of drama. The word named a structural relationship — the foundation to the superstructure, the specific to the general, the given to the derived.

In Greek philosophy, hypóthesis was used for the starting assumptions of a mathematical or philosophical argument — the unproved premises that the reasoning took for granted. Plato uses the term in this sense in the Meno and the Republic: a hypothesis was a supposition made provisionally in order to see what would follow from it, not a proven truth but an assumed starting point. Euclid's geometry proceeds from hypotheses (postulates and axioms), statements accepted without proof as the foundation of the entire deductive system. The mathematical hypothesis was not tentative in the sense of being doubtful — it was foundational in the sense of being prior to proof rather than following from it. The supposition came first; everything else was built on top.

The scientific method transformed the meaning of hypothesis into something more provisional and more testable than either its rhetorical or its mathematical sense. In the Baconian and later Newtonian conception of scientific investigation, a hypothesis was an explanatory proposition offered as a possible account of observed phenomena, subject to testing against further observation. Newton's famous phrase 'hypotheses non fingo' ('I frame no hypotheses') in the Principia expressed his refusal to speculate beyond what his mathematics and observations could support — though the phrase is ironic, since his theory of gravity was itself a hypothesis in the broader sense. The scientific hypothesis was distinguished from a mere guess by its testability: a good hypothesis made specific predictions that could be verified or refuted.

The modern scientific use of 'hypothesis' has settled into a precise technical meaning: a proposed explanation for an observation, formulated in a way that allows it to be tested by experiment. The hypothesis comes before the theory: where a theory is a well-supported explanation for a wide range of phenomena, a hypothesis is the provisional proposal that precedes the evidence. This ordering reflects the structure of the word's origin — the hypothesis is placed underneath, prior and foundational, waiting to be supported or rejected by what is built on top of it. The Greek architectural metaphor has become a methodological prescription: you cannot build without a foundation, and the foundation must be placed first, before you know whether it will hold.