Which characteristic defines a derivational morpheme?

A derivational morpheme is defined primarily by its ability to modify meaning and create new words. When a derivational morpheme is added to a base word, it often alters the original meaning and may change the word's part of speech. For example, adding the suffix “-ness” to the adjective “happy” forms the noun “happiness,” thus demonstrating how derivational morphemes can transform and expand vocabulary by creating new terms.

While some of the other characteristics mentioned have validity in discussing morphemes, they do not accurately define derivational morphemes specifically. For instance, a morpheme that only alters the tense of a verb pertains more to inflectional morphemes, which do not create new words but modify existing ones for grammatical purposes. Furthermore, the notion that a morpheme cannot stand alone applies broadly to many morphemes, but standalone capability is not a defining characteristic of derivational morphemes. Lastly, the representation of the subject of a sentence relates to grammar rather than morpheme classification. Thus, the ability of derivational morphemes to create new words while modifying meaning is a key feature that distinctly defines them.