text: Generally speaking, inflection applies in more or less regular patterns to all members of a part of speech (for example, nearly every English verb adds -s for the third person singular present tense), while derivation follows less consistent patterns (for example, the nominalizing suffix -ity can be used with the adjectives modern and dense, but not with open or strong).  However, it is important to note that derivations and inflections can share homonyms, that being, morphemes that have the same sound, but not the same meaning.  For example, when the affix -er, is added to an adjective, as in small-er, it acts as an inflection, but when added to a verb, as in cook-er, it acts as a derivation.
  A derivation can produce a lexeme with a different part of speech but does not necessarily. For example, the derivation of the word "uncommon" from "common" + un- (a derivational morpheme) does not change its part of speech (both are adjectives).
  An important distinction between derivational and inflectional morphology lies in the content/function of a listeme. Derivational morphology changes both the meaning and the content of a listeme, while inflectional morphology doesn't change the meaning, but changes the function.
  A non-exhaustive list of derivational morphemes in English: -ful, -able, im-, un-, -ing, -er
  A non-exhaustive list of inflectional morphemes in English: -er, -est, -ing, -en, -ed, -s
  Derivation and other types of word formation
  Derivation can be contrasted with other types of word formation such as compounding.