# Supposition
## Overview
**Supposition** means an idea assumed to be true for the purpose of argument, even without conclusive evidence. It is a working hypothesis — something 'placed under' a line of reasoning to support it.
## Etymology
From Old French *suposicion*, from Latin *suppositionem* (accusative of *suppositio*, 'a placing under, substitution'), from *suppositus*, past participle of *supponere* ('to put under, place beneath'), composed of *sub-* ('under') and *ponere* ('to put, place').
Latin *ponere* ('to put, place') — from its past participle *positus* — is one of the most prolific verb roots in English. Combined with different prefixes, each directing the 'placing' in a different way, it generates an enormous vocabulary:
| Word | Prefix + ponere | Literal meaning | |------|----------------|----------------| | **Position** | *positio* | a placing | | **Compose** | *com-* (together) | to place together | | **Deposit** | *de-* (down) | to place down | | **Expose** | *ex-* (out) | to place out | | **Impose** | *in-* (upon) | to place upon | | **Oppose** | *ob-* (against) | to place against | | **Propose** | *pro-* (forward) | to place forward | | **Dispose** | *dis-* (apart) | to place apart | | **Suppose** | *sub-* (under) | to place under | | **Transpose** | *trans-* (across) | to place across | | **Postpone** | *post-* (after) | to place after | | **Purpose** | *pro-* (before) | to place before oneself |
Each produces its own noun family: composition, deposition, exposition, imposition, opposition, proposition, disposition, supposition, transposition, and so on.
## Supposition in Logic
In formal logic, a **supposition** (or **assumption**) is a statement accepted as true within a particular argument or proof, without requiring independent demonstration. The technique of 'supposing for the sake of argument' allows reasoning to proceed from unproven premises to test their implications.
In medieval logic, *suppositio* was a technical term for how a term in a proposition 'stands for' its referent — a theory of reference that anticipated modern semantic analysis.
## Related Forms
The family includes **suppose** (verb), **supposed** (adjective, 'believed to be'), **supposedly** (adverb), **presuppose** (to suppose in advance), and **presupposition** (a prior assumption). The phrase 'on the supposition that' introduces a conditional premise.