LET English Practice Exam

A derivational morpheme is a type of morpheme that, when added to a base word, changes the meaning or the part of speech of that word. In this case, the prefix "un-" in "unhappy" is a derivational morpheme because it alters the meaning of the root word "happy" to create its opposite. By adding "un-," the new word expresses a different concept, indicating a negative state.

In contrast, the other examples illustrate inflectional morphemes, which modify a word to express grammatical relationships but do not change the underlying meaning of the word itself. For instance, the suffix "-ed" in "walked" indicates past tense, and "-ing" in "running" indicates the present participle form. The "s" in "cats" shows pluralization but does not transform the noun into a different part of speech or alter its fundamental meaning. Thus, "un-" effectively exemplifies the characteristics of a derivational morpheme.