Derivational morpheme: a morpheme which can be derived (added) to another morpheme to create a new word (such as adding -ness to happy to form the new word happiness) Inflectional morpheme: a morpheme which can change a word's tense, number, etc. (such as adding -s to dog to form the plural dogs)

For example, in the word happiness, the addition of the bound morpheme -ness to the root happy changes the word from an adjective (happy) to a noun (happiness). In the word unkind, un-functions as a derivational morpheme since it inverts the meaning of the root morpheme (word) kind. Generally, morphemes that affix (i.e., affixes) to a root ...

However, derivational morphemes often change the part of speech of a word. Thus, the verb read becomes the noun reader when we add the derivational morpheme -er. It is simply that read is a verb, but reader is a noun. However, some derivational morphemes do not change the grammatical category of a word.