What do derivational morphemes do to a word?

Derivational morphemes are affixes that modify a base word in a way that often results in a change of its grammatical category or its meaning. For instance, adding the suffix "-ly" to the adjective "quick" transforms it into the adverb "quickly," effectively changing its word class from an adjective to an adverb while also extending its meaning. Similarly, the prefix "un-" can be added to the adjective "happy" to create "unhappy,” shifting its meaning entirely. This fundamental role in language allows for the formation of new words and concepts while enriching the vocabulary.

The option regarding extending the meaning of the word is a component of what derivational morphemes do but does not capture the primary function of changing word categories. Combining two words into one pertains more to compounding than derivational morphology, and altering emotional connotation can occur as a semantic effect but is not a defining characteristic of derivational morphemes specifically. Thus, the focus on changing the category or meaning best encapsulates the essence of how derivational morphemes operate within a language.