An idea or theory that is assumed to be true for the purpose of argument or investigation, but without definitive proof. It represents a hypothesis or conjecture that serves as a starting point for reasoning or testing.
From Latin 'suppositio' meaning 'a placing under, substitution', derived from 'supponere' (to place under, substitute). The root combines 'sub-' (under) and 'ponere' (to place). The metaphor suggests placing an idea 'under' or as the foundation for further thinking, entering English in the 14th century.
Supposition is the engine of scientific discovery - every great breakthrough started as a 'what if' that someone was willing to suppose might be true! Unlike assumptions (which we often don't realize we're making), suppositions are conscious hypotheses that we deliberately entertain to explore possibilities.
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