1. Primary: added to the root, or (in later times by analogy) to verb-stems.
2. Secondary: added to a noun-stem or an adjective-stem.
Both primary and secondary suffixes are for the most part pronominal roots (§ 228. 2), but a few are of doubtful origin.
NOTE 1: The distinction between primary and secondary suffixes, not being original (see § 227), is continually lost sight of in the development of a language. Suffixes once primary are used as secondary, and those once secondary are used as primary. Thus in hosticus (hosti cus) the suffix -cus, originally ko- (see § 234. II. 12) primary, as in paucus, has become secondary, and is thus regularly used to form derivatives; but in pudícus, aprícus, it is treated as primary again, because these words were really or apparently connected with verbs. So in English -able was borrowed as a primary suffix (tolerable, eatable), but also makes forms like clubbable, salable; -some is properly a secondary suffix, as in toilsome, lonesome, but makes also such words as meddlesome, venturesome.
NOTE 2: It is the stem of the word, not the nominative, that is formed by the derivative suffix. For convenience, however, the nominative will usually be given.