In the field of linguistics, particularly in the minimalist program, Logical Form (abbreviated LF), refers to a mental representation of a linguistic expression, derived solely from Surface Structure. In the words of Chomsky, LF captures "those aspects of semantic representation that are strictly determined by grammar, abstracted from other cognitive systems".[1] LF is the semantic equivalent of Phonetic Form (PF), a representation of the sound of a sentence derived from its surface structure.
Logical form is the level of representation which fully determines the semantics of a sentence. LF is sometimes referred to as a covert level of representation, because the output of this level is not actually pronounced by the speaker.[2] LF is posited in syntax in order to give a structural account of certain kinds of semantic ambiguities. For example, the sentence,
is semantically ambiguous. Specifically, it contains a scope ambiguity. This ambiguity cannot be resolved at surface structure, since someone, being within the verb phrase, must be lower in the structure than everyone. This case exemplifies the general fact that natural language is insufficiently specified for strict logical meaning.[3] Noam Chomsky and his student Robert May argued for the postulation of LF partly in order to account for such ambiguities (among other motivations).[3] At LF, the sentence above would have two possible structural representations, one for each possible scope-reading, in order to account for the ambiguity by structural differentiation. In this way it is similar in purpose to, but not the same as, Logical form in logic.[4]
Generative semanticists, however, have argued that ambiguities like the one in the example above should be resolved at deep structure (or at least, some level of representation preceding surface structure in the derivation), in order to avoid positing covert movement.[5]