In a speech-language therapy session, Angela, a speech-language pathologist, is working with Lucas, a 7-year-old child who is struggling with morphological development. Lucas has difficulty modifying words to express more complex meanings, such as turning a verb into a noun or adjusting the tense of a word. Angela is helping him understand how morphemes, the smallest units of meaning in language, work. She explains that some morphemes are derivational in nature, which means they can be added to a base word to change its meaning or part of speech. Angela then asks Lucas and his parents to identify the purpose of these types of morphemes that can modify the structure of a word to create a new meaning.

What is the function of derivational morphemes?