In some theories of syntax and grammar, in particular in the Chomskyan schools of Government and Binding Theory and 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". It functions as the interface between grammar and conceptual-intentional properties of language, analogous to how the Phonetic Form (abbreviated PF) is the interface between grammar and the audio-perceptual properties of utterances.

The logical form of a sentence (or proposition or or truthbearer) or set of sentences is the form obtained by abstracting from the subject matter of its content terms or by regarding the content terms as mere placeholders or blanks on a form. In an ideal logical language, the logical form can be determined from syntax alone; formal languages used in formal sciences are examples of such languages. Logical form, however, should not be confused with the mere syntax used to represent it; there may be more than one string that represents the same logical form in a given language.