As we noted in Chapter 15, sentences convey information not expressed by words in isolation. Which person or object is accomplishing an action, which is receiving an action, where actions are taking place, and similar information – known as “thematic roles” – is not part of the lexical semantic information associated with each word, but rather depends upon the relationship of words to each other within a sentence. Similarly, sentences convey the information of which adjectives and other modifiers are associated with which nouns, how pronouns are related to nouns, and other aspects of meaning. When we understand speech, we must extract this “sentential” and “phrasal” semantic information from the sentences that we hear, or we have failed to understand a significant part of the information conveyed by spoken language.

There is a fundamental difference between the way sentential semantic information is represented in sentences and the way lexical semantic information is associated with individual words. For a simple lexical item, essential semantic information must be connected in a direct fashion to the representation of the word in a mental lexicon. We have seen in Chapters 12, 13, and 14 that accessing the mental lexicon from sound or print is not a simple process, nor is accessing a semantic representation from the mental lexicon. Despite the complexity of the processes involved in identifying words and recovering the meaning of a word, the meaning of a word is “directly” associated with its form, in the sense that each word has one meaning (except homophones, homographs, and ambiguous words).