In generative grammar and related approaches, the logical form (LF) of a linguistic expression is the variant of its syntactic structure which undergoes semantic interpretation. It is distinguished from phonetic form, the structure which corresponds to a sentence's pronunciation. These separate representations are postulated in order to explain the ways in which an expression's meaning can be partially independent of its pronunciation, e.g. scope ambiguities. LF is the cornerstone of the classic generative view of the syntax-semantics interface. However, it is not used in Lexical Functional Grammar and Head-Driven Phrase Structure Grammar, as well as some modern variants of the generative approach. Syntax interfacing with semantics The notion of Logical Form was originally invented for the purpose of determining quantifier scope. As the theory around the Minimalist program developed, all output conditions, such as theta-criterion, the case filter, Subjacency and binding theory, are examined at the level of LF. The study of LF is more broad than the study of syntax. The notion of scope The scope of an operator is the domain within which it has the ability to affect the interpretation of other expressions. In other words, an operator has scope of operation, or affecting the interpretation of other phrases, only within its own domain. Three uncontroversial examples of scope affecting some aspect of the interpretation are: quantifier-quantifier, quantifier-pronoun, quantifier-negative polarity item. In instances where a negation has an indefinite article in its scope, the reader's interpretation is affected. The reader is not able to infer the existence of a relevant entity. If negation (or a negation phrase) is within the subject quantifier scope, negation is not affected by the quantifier. If the Quantified Expresstion1 (QE1) is in the domain of QE2, but not vice versa, QE1 must take a narrow scope; if both are in the domain of the other, the structure is potentially ambiguous. If neither QE is in the domain of the other, they must be interpreted independently. These assumptions explain the cases where the direct object of the main clause is not within the domain of the embedded subject. For example, that every boy left upset a teacher, it cannot be interpreted as for every boy, there is a possibly different teacher who was upset by the fact that the boy left. The only available interpretation is that one single teacher was upset. Ambiguity motivation In syntax, LF exists to give a structural account