premise
Synonym discussion
Sense: noun/1
For noun/1, premise is a formal word for a statement or idea used as the starting point in reasoning. Assumption is broader and more common in everyday English; it can be any belief accepted without proof. Basis is wider still, because it may be a fact, reason, or support rather than a clearly stated claim. Principle usually means a general rule or moral belief, not one step in an argument. In debate, logic, and academic writing, premise is the most exact choice when you want to focus on the idea a conclusion grows from. You can say The study rests on the assumption that sleep helps memory, but The argument fails because its first premise is false.
Etymology
'Premise' came into English in the late Middle English period through Old French and Medieval Latin from the Latin verb praemittere, meaning 'send before' or 'put before'. Early uses referred to something stated in advance, which matches the modern noun sense of a starting statement or assumption. The verb later developed from the noun and kept the same idea of building later reasoning on something placed first.