Semantic Relations

A verb is related in various ways to the constituents in a sentence. The relations depend on the meaning of  the particular verb. For example the NP the girl in the girl found a red brick is called agent or ‘doer’ of the action of finding. The NP a red brick is the patient or ‘recipient’ of the action. Part of the meaning of find is that its subject is as an agent and its logical object is a patient. That fact is reflected in the entry for find in the lexicon.

            The noun phrases that follow the verb put have the relation of patient and location. In the verb phrase put the red brick on the wall, the red brick is the patient and on the wall is the location. The entire verb phrase is interpreted to mean that the patient of put changes its position to the location. The location, itself a prepositional phrase, will have its own meaning, which is combined with the meaning of put and the meaning of the red brick. Put’s subject is also an agent, so that in the girl put the red brick on the wall, ‘the girl’ performs the action. Semantic rules do all this work, revealing speaker knowledge about the meaning of such sentences.

            The semantic relationships that we have called patient, agent, and location, are among the semantic relations of the verb. Other semantic relations are goal, where the action is directed, source, where the action originated, and instrument, an object used to accomplish the action. Consider the following example:

                        The girl carried the red brick from the wall to the wheelbarrow.

The girl is the agent; the red brick is the patient; the wall is the source; the wheelbarrow is the goal. In

                        The girl broke a window with the red brick.

the girl is again the agent, a window is the patient, and the red brick is the instrument. These examples show that the same noun phrase (the red brick) can function in a different semantic role depending on the sentence.

            The lexical entries for find and put would now look something like the following:

                        Find, V, ̶  NP, (Agent, Patient)

                        Put, V, ̶  NP PP, (Agent, Patient, Location)

The semantic relations are contained in parentheses. The first one states that the logical subject is an agent. The remaining semantic relations belong to the constituents for which the verb is subcategorized. The logical object of both find and put will be a patient. The prepositional phrase for which put subcategorized will be location.  

            Our knowledge of verbs includes their syntactic category, how they are subcategorized, and the semantic relations that their noun phrase  subject and object(s) have, and his knowledge is explicitly represented  in the lexicon.

            Semantic relations are the same in sentences that are paraphrases. In both these sentences

                        The dog chased the cat.

                        The cat was chased by the dog.

the dog is the agent and the cat is the patient.

            Semantic relation may remain the same in sentences that are not paraphrases, as in the following instances;

                                    The owner opened the door with the key.

                                    The key opened the door.

                                    The door opened.

In all three of these sentences, the door is the patient, the thing that gets opened. In the first two sentences, the key, despite its different structural role, retains the semantic role of instrument.

            In many languages semantic roles are reflected in the case assumed by the noun. The case or grammatical case of a noun is the particular morphological shape that it takes. English nouns do not have extensive case, but the possessive form of a noun, as in girl’s red brick, is called the genitive or possessive case.

            In other languages such as Finnish, the noun assumes a morphological shape according to its semantic role in the sentence. For example, in Finish koulu- is the root meaning ‘school’, and –sta is a case ending that means ‘directional  source’. Thus koulusta means ‘from the school’. Similarly, kouluun (koulu +un) means ‘to the school’.

            Some of the information carried bt grammatical case in languages like Finnish is borne by prepositions in English. Thus from and to often indicate the semantic relations of source and goal. Instrument is marked by with, location by prepositions such as on and in, and agent by by in passive sentences. The role of patient is generally accompanied by a preposition, as is agent when it is the structural subject of the sentence. What we are calling semantic relations or roles in this section has sometimes been studied as case theory.