optional (adj.)

A term in LINGUISTICS which refers to an ELEMENT that can be removed from a STRUCTURE without that structure becoming UNGRAMMATICAL. In the sentence I saw the pen on the desk, on the desk is an optional ADVERBIAL. In early TRANSFORMATIONAL grammar, the term refers to one of two types of RULE postulated by Noam Chomsky in his book Syntactic Structures (1957), the other being OBLIGATORY. Optional transformations may apply at a certain stage in a DERIVATION; but it is not essential for the WELL-FORMEDNESS of the SENTENCE that they do so, e.g. the transformation from POSITIVE to NEGATIVE, ACTIVE to PASSIVE, or DECLARATIVE to INTERROGATIVE. In later versions of transformational GRAMMAR, the range of this notion changes, as more structural rules come to be incorporated into the BASE component of the grammar, and are thus handled by obligatory rules. A few rules handling STYLISTIC alternatives remain optional.