Premise

A premise is a proposition offered to support a conclusion. Premises are true or false statements that act as the starting points of arguments by presenting reasons to substantiate or refute assertions. Each argument is made up of a set of premises together with a conclusion. For example, the premises "all men are mortal" and "Socrates is a man" guarantee the conclusion "Socrates is mortal". In ordinary language, premises can appear in the middle of a passage, often marked by indicator words, such as since and because. In formal logic, a common approach is to write each premise on a separate line, known as standard form.

Different types of premises are distinguished by their form of expression, their role in arguments, and their content. Explicit premises are overtly stated, whereas implicit premises are tacitly assumed without appearing in the text, often involving uncontroversial common-sense information shared by speaker and audience. Independent premises present distinct reasons, providing separate support for the conclusion. They contrast with dependent premises, which only work in combination. Other distinctions concern whether premises appear as first or intermediate steps in arguments, whether they are affirmative or negative, whether they refer to specific entities or make general claims, whether they are descriptive or normative, and what internal structure they have.

The role of premises in arguments is typically either to preserve truth when drawing a conclusion, or to transfer justification from accepted statements to the claim for which one is arguing. To succeed, premises must be true or justified and must be relevant to the conclusion. The premises of deductively valid arguments provide the strongest support: if the premises are true, then the conclusion cannot be false. The premises of non-deductive arguments aim to make the conclusion more reasonable or increase its probability, such as inductive, abductive, and analogical arguments. Defective arguments, called fallacies, can often arise from faulty premises. For example, premises may contain false information, confuse the audience with irrelevant details, or use ambiguous terms that mislead by shifting meaning. Premises are central to many fields, including logic, argumentation theory, mathematics, philosophy, science, and law.