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.
Definition
Premises are propositions offered to support a conclusion. They are assumptions or commitments that serve as the starting points of logical reasoning by presenting considerations to justify or refute standpoints. Each argument is made up of a set of premises together with a conclusion. For example, the argument "All men are mortal. Socrates is a man. Therefore, Socrates is mortal" has two premises ("All men are mortal" and "Socrates is a man") followed by a conclusion ("Therefore, Socrates is mortal").
As a proposition or statement, each premise is either true or false, in contrast to other types of sentences, such as questions and commands. While all premises are propositions, not all propositions function as premises: some serve as conclusions or occur outside arguments. For example, passages that simply report observations, illustrate ideas, or explain events can include statements that do not serve as premises. Premises are further distinguished from theses, which are statements someone aims to justify. Theses are similar to hypotheses, which are tentative assumptions in scientific practice that guide research and are tested by experiments. By contrast, a statement has to be offered as a reason for a conclusion to count as a premise. The strength of an argument depends on how well the premises support the conclusion. True premises can support a conclusion if they are relevant to it, whereas false premises offer no support.
The word premise comes from the Latin term , meaning , which has its roots in the preposition () and the verb (). It gave rise to the Latin term (), which was borrowed into Old French as the word in the 14th century. The Old French term entered Middle English with the earliest evidence of use in the late 14th century. Outside its main meaning in discourse, logic, and science, the term premises refers to a piece of land and the buildings on it. Another meaning is found in narrative theory, where the premise of a plot is the foundational idea around which the story revolves.
Identification of premises The ability to identify premises is central to understanding and assessing arguments. In ordinary language used in everyday discourse, arguments often lack a consistent or standard formal structure: the conclusion may appear before, between, or after the premises, without a fixed order to indicate whether a statement is a premise or a conclusion. This can obscure logical relationships between statements and lead to misinterpretation, particularly in complex arguments involving intertwined premises and nested sub-arguments. One way to identify premises is to look for premise indicatorsverbal cues that signal where a premise begins, such as since, because, given that, and as implied by. For example, the argument "she is not at home since she has gone to the shop" begins with a conclusion and uses the term since to mark where the premise starts. However, indicator words are not always present, and even when they are, their context-dependent meaning does not guarantee that the statements they introduce are premises.
To analyze and evaluate ordinary-language arguments, logicians usually try to paraphrase them in the standard form to disambiguate their components and clarify their logical structure without reyling on context-dependent premise indicators. The standard form presents each premise on a separate line, with the conclusion on the last line. A horizontal bar is often placed between the premises and the conclusion, as in:
If Luis went to the dance, then Bernadette went to the dance. Luis went to the dance. ────────────────────────────────────── Bernadette went to the dance.
In formal logic, premises and conclusions are typically expressed through symbols that represent propositions and their relations. For example, using the symbols for "Luis went to the dance", for "Bernadette went to the dance", and for "if ... then ...", the argument can be written as:
──────
Types Philosophers discuss various types of premises, distinguished by their mode of expression, their role in arguments, and their content.
Explicit and implicit Explicit premises are overtly stated in an argument. They are claims that appear directly in the text and function as the main reasons supporting the conclusion. By contrast, implicit or tacit premises are not directly stated but merely implied. Also called enthymematic premises, they function as background assumptions that link the explicit premises to the conclusion. For example, the argument "you should not drink that milk because it is expired" has the explicit premise "the milk is expired" while assuming the implicit premise that people should not drink expired milk.
Implicit premises are common in ordinary-language arguments because speakers often omit uncontroversial common-sense information shared with their audience. This practice focuses attention on essential points by omitting obvious or redundant details, promoting efficiency and concision. However, implicit premises can obscure key points or conceal contentious assumptions, confusing the audience by leading them to misinterpret the speaker's position or by making a weak argument look stronger than it is. A key interpretive tool for handling implicit premises is the principle of charity, which recommends selecting the most reasonable statements for the missing premises to reconstruct the strongest version of the argument.
Independent and dependent
Two premises are independent if they present distinct reasons. Also called convergent or coordinate premises, they provide separate support for the conclusion. For example, the argument "I should not buy these shoes because they are too small and too expensive" cites two independent premises for distinct considerations: size and price. Since the premises offer separate reasons, one would still provide some support for the conclusion if the other was removed. Multiple independent premises are often needed when the support from a single premise is not sufficiently strong to establish the conclusion beyond a reasonable doubt. For example, prosecutors in criminal cases may provide a list of independent premises for the defendant's guilt, such as a motive to commit the crime, ownership of the murder weapon, fingerprints at the crime scene, and a lack of alibi.
Two premises are dependent if they work only in combination. Also called joint or linked premises, they function together to present a single reason for the conclusion. For instance, the argument "This song will either be an enormous success or an utter failure. It will not be an enormous success. Therefore, it will be an utter failure" has two premises: one states that there are only two options, and the other rules out one option, leaving the other option as the only candidate. These premises are dependent because neither can support the conclusion alone: the first one does not indicate which option is correct, and the second one leaves open the possibility of a moderate success. Dependent premises are common in deductive reasoning where each premise is often essential for the conclusion.
Axioms and intermediate premises
Axioms are initial assumptions used as first premises in reasoning. In logical systems, they serve as foundational statements from which other statements, called theorems, are derived. For example, a central axiom in Euclidean geometry states that for any two distinct points, there exists a unique line passing through them. Not all premises are axioms, and some premises function as intermediate steps in complex arguments and proofs, as in the following chain of reasoning: "I could not find the keys in the kitchen. Therefore, they are not in the kitchen. They are either in the kitchen or in the bedroom. Therefore, they are in the bedroom." In this example, the statement "they are not in the kitchen" is the conclusion of the first argument and a premise of the second.
Others Premises can also be classified by the type of statement they express. Affirmative premises assert that something is the case (e.g. Laika was a dog), whereas negative premises deny that something is the case (e.g. Jumbo was not a dog). Universal statements claim that something holds for all entities, while existential statements assert that something holds at least for one entity, and singular propositions talk about one specific entity, as in the contrast among "all men are mortal", "some men are mortal", and "Aristotle is mortal". Simple premises consist of a single proposition, whereas compound premises combine several propositions. For example, disjunctive premises use the connective or to express that at least one of several propositions is true, conjunctive premises use the connective and to express that all of several propositions are true, and conditional or hypothetical premises are made up of two propositions linked through an if-then relationship.
Premises can also be distinguished by their content. Descriptive premises state what is the case, whereas prescriptive or normative premises are about what should be the case. This distinction plays a central role in Hume's lawthe thesis that purely descriptive premises cannot support normative conclusions. According to this view, arguments such as "Humans have carnivorous teeth. Therefore, they should eat meat." commit fallacies by concluding what should be from what is.