initial symbol

The first, undefined term in a GENERATIVE GRAMMAR, employed in early PHRASE-STRUCTURE GRAMMARS, which appears on the left-hand side of the first REWRITE RULE. Standing for SENTENCE, the highest-level CONSTRUCTION recognized by the grammar, it has been symbolized as Σ, S′ or CP. The contrast implied is with TERMINAL symbols, the items which occur in a terminal STRING generated by the grammar. Other starting-points than sentence have occasionally been suggested.