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Definition of LOGIC
a (1): a science that deals with the principles and criteria of validity of inference and demonstration : the science of the formal principles of reasoning (2): a branch or variety of logic <modal logic><Boolean logic>(3): a branch of semiotics; especially:syntactics(4): the formal principles of a branch of knowledge
Study of inference and argument. Inferences are rule-governed steps from one or more propositions, known as premises, to another proposition, called the conclusion. A deductive inference is one that is intended to be valid, where a valid inference is one in which the conclusion must be true if the premises are true (seededuction; validity). All other inferences are called inductive (seeinduction). In a narrow sense, logic is the study of deductive inferences. In a still narrower sense, it is the study of inferences that depend on concepts that are expressed by the logical constants, including: (1) propositional connectives such as not, (symbolized as ¬), and (symbolized as ), or (symbolized as ), and if-then (symbolized as ), (2) the existential and universal quantifiers, (x) and (x), often rendered in English as There is an x such that and For any (all) x, , respectively, (3) the concept of identity (expressed by =), and (4) some notion of predication. The study of the logical constants in (1) alone is known as the propositional calculus; the study of (1) through (4) is called first-order predicate calculus with identity. The logical form of a proposition is the entity obtained by replacing all nonlogical concepts in the proposition by variables. The study of the relations between such uninterpreted formulas is called formal logic. See alsodeontic logic; modal logic.