Of the three levels in (2) [immagine], the first level comprises the affixes which have usually been associated with the + boundary. They correspond to the "primary suffixes" of traditional description [...]. This level includes derivational suffixes such as "-al, -ous, -ity, -th", and inflectional suffixes such as those in "kept, met, hidden, children, addenda, indices, foci" as well as "ablaut", "umlaut", and other stem-changing morphology as in "teethe, bleed, bathe, teeth, lice". To the second level we assign #-boundary ("secondary") derivation and compounding. [...] The third level takes care of the remaining, "regular" inflection ("leaped, pleated, books, conundrums, indexes, crocuses", etc.) [...].
- Kiparsky (2004), a pag.96