A premise or premiss[a] is a statement that an argument claims will induce or justify a conclusion. In other words: a premise is an assumption that something is true. In logic, an argument requires a set of (at least) two declarative sentences (or "propositions") known as the premises or premisses along with another declarative sentence (or "proposition") known as the conclusion. This structure of two premises and one conclusion forms the basic argumentative structure. More complex arguments can use a series of rules to connect several premises to one conclusion, or to derive a number of conclusions from the original premises which then act as premises for additional conclusions. An example of this is the use of the rules of inference found within symbolic logic.
Aristotle held that any logical argument could be reduced to two premises and a conclusion. Premises are sometimes left unstated in which case they are called missing premises, for example:
Socrates is mortal because all men are mortal.
It is evident that a tacitly understood claim is that Socrates is a man. The fully expressed reasoning is thus:
Because all men are mortal and Socrates is a man, Socrates is mortal.
In this example, the independent clauses preceding the comma (namely, "all men are mortal" and "Socrates is a man") are the premises, while "Socrates is mortal" is the conclusion.
The proof of a conclusion depends on both the truth of the premises and the validity of the argument.
^In logic, premise and premiss are regarded as variant spellings of the same word, premise being the more common spelling.Charles Sanders Peirce (1839–1914) argued that premise and premiss are two distinct words, writing "As to the word premiss,—in Latin of the thirteenth Century praemissa,—owing to its being so often use in the plural, it has become widely confounded with a totally different word of legal provenance, the 'premises,' that is, the items of an inventory, etc., and hence buildings enumerated in a deed or lease. It is entirely contrary to good English usage to spell premiss, 'premise,' and this spelling...simply betrays ignorance of the history of logic."
^"Argument: a sequence of statements such that some of them (the premises) purport to give reasons to accept another of them, the conclusion" : The Cambridge Dictionary of Philosophy, 2nd Edition (Cambridge University Press), editor Robert Audi, 43.