The following article is an attempt to formulate some principles for the structural description of a language. ] They have been used successfully to characterize the expression systems of half a dozen Philippine languages (Tagalog, Bicol, lbanag, Pampango, Waray, and Cebuano) and English, and may thus be said to be adequate at least for these languages. The discussion which follows is divided into three parts: I - the nature of description in general, II - the nature of the object of a linguistic structural description in particular, and III - a proposed descriptive formalism.