premiss

Premiss, also spelled premise in American English, is the statement in an argument that is taken to be true and used to derive a conclusion. In logic and philosophy, premises provide the evidentiary basis for an inference. A single premise may be enough for a simple deduction, but most arguments rely on two or more premises that, together, support the conclusion.

Premisses can be explicit or implicit; an author may assume a premise without stating it. In a syllogism, premises are propositions from which a middle term is inferred to the conclusion. The term has spelling variations: premiss is the traditional or British spelling; premise is more common in American English; the plural of premiss is premisses, while the plural of premise is premises, which also means a building or property.

Example: Premises: All humans are mortal. Socrates is a human. Therefore Socrates is mortal.

Notes: If a premise is false, the argument may be unsound; even if the argument is valid, false premises can invalidate the conclusion. In modern usage, many writers prefer 'premise' for the proposition, while 'premiss' appears primarily in older texts or certain stylistic traditions.