studies of the rules for forming admissible sentences
<noun.cognition>
Syntax \Syn"tax\, n. [L. syntaxis, Gr. ?, fr. ? to put together in order; sy`n with + ? to put in order; cf. F. syntaxe. See {Syn-}, and {Tactics}.] 1. Connected system or order; union of things; a number of things jointed together; organism. [Obs.]
They owe no other dependence to the first than what is common to the whole syntax of beings. --Glanvill.
2. That part of grammar which treats of the construction of sentences; the due arrangement of words in sentences in their necessary relations, according to established usage in any language.
So time isn't wasted searching the entire vocabulary, Sphinx takes syntax into account.