173. Every proposition is a sentence, but every sentence is not a
proposition.

174. The field of logic is far from being conterminous with that of
language. Language is the mirror of man's whole nature, whereas logic
deals with language only so far as it gives clothing to the products
of thought in the narrow sense which we have assigned to that term.
Language has materials of every sort lying strewn about, among which
the logician has to seek for his proper implements.

175. Sentences may be employed for a variety of purposes--

(1) To ask a question;

(2) To give an order;

(3) To express a feeling;

(4) To make a statement.

These various uses give rise respectively to

(1) The Interrogative Sentence;

(2) The Imperative Sentence;

(3) The Exclamatory Sentence;

(4) The Enunciative Sentence; Indicative Potential.