Introduction to semantic roles
Semantic roles are parts that participants play in certain circumstances (Dang & Palmer, 2005, p.42). They express the relationship that a constituent has with the rest of the clause. The main verbs in a clause are normally responsible for expressing this relationship. Semantic roles include; agents, patients, location, instruments, causer, experiencer, theme, benefactee, source, and goal (2005, p.43).
An agent is the participant that the verb describes as doing or intentionally causing something (Gildea & Jurafsky, 2002,p.249).
Kim ate the food hurriedly.
The boy hit the wall.
In the sentences above, Kim and the boy are the agents. Kim does the act of eating while the boy intentionally hits the wall.
The causer, on the other hand, is the participant that the verb identifies as causing something but not intentionally (Gildea & Jurafsky, 2002,p.250). In the examples shown below, the stone does not have any intention to destroy the house; neither does the fire in burning the crops.
The stone destroyed the house.
The fire burnt the crops.
According to Gildea and Jurafsky (2002, p.250), the instrument is the medium which the agent uses to carry out the action the predicator denotes. The bat in the sentence below is the instrument.
Humphrey hit the ball with a bat.
The experiencer is the participant who is aware of something or experiencing something. This participant is normally animate and unintentionally perceives sensory stimuli or state of mind (Gildea & Jurafsky, 2002, p.251).
The student felt uncomfortable in church.
The student unintentionally feels bad while in church.
The patient is the participant to whom an action happens (Gildea, & Jurafsky, 2002,p.249). The action that the verb denotes affects the patient. In the sentence “The boy hit the ball,” The ball is the patient because the action of hitting affects it directly.
Gildea and Jurafsky (2002, p.249) define a theme as the participant whom the verb describes as being dynamic or in a state or position. “Post” is the theme in this sentence.
The post rolled into the river.
The Recipient is an endpoint of the act of transferring an item (Gildea & Jurafsky, 2002, p.249). John is the recipient in this sentence. He receives a letter from Amos.
Amos sent a letter to John.
The Benefactee is the participant who benefits from the results of an action (Gildea & Jurafsky, 2002, p.249). John is a benefactee in this sentence. John benefits from the act of buying the shirt.
I bought a nice shirt for John.
Location is normally a noun phrase that specifies the position of an item (Gildea & Jurafsky, 2002,p.250). A location verb normally accompanies the agent in specifying this position. In the sentence, “Jim put his books on the table.” “Put” is the verb of location while the table is the location.
The source is the participant from which motion originates. It is, therefore, the starting point of a movement or action (Gildea & Jurafsky, 2002, p.250). When someone says, “We expect to get a loan from the bank.” Then “the bank” becomes the source in this sentence.
Gildea and Jurafsky (2002, p.249) define the goal as the destination or the end point of a movement or an action. The bank is the goal in the sentence below since the participants direct their action towards the bank.
We took the director to the bank to withdraw money for the salaries.
Semantic roles and Passive constructions
The GB theory argues that there is a similarity in both active and passive constructions (Black, 1999, p.29). According to this theory, the semantic roles of the lexicons in the sentence can help bring out these similarities in active and passive constructions. This means every constituent has a semantic role and an extra role for the subject (1999, p.30). The theory further observes that some verbs do not give a semantic role to the position of the subject.
The GB theory also proposes that forms that relate to each other share a sub categorization frame and, therefore, there ought not to be cross linking of semantic roles and syntactic categories.
This means that it is a crime to assign the theme to both the subject and the object in entries that relate to each other (1999). Black (1999, p.30) argues that the theme is always the direct object while the indirect object is always the recipient.
Another assumption allows an item to move out of a position but forbids the replacement of another item in that position (Black, 1999, p.30). This, therefore, means, the semantic role remains in its former position and does not move with the outgoing phrase. The semantic role is, therefore, a constituent of the lexical sub categorization (1999, p.30).
This theory forbids an element from moving into a position that relates to a semantic role because it makes the new occupant of the position take over that role, thus changing the linking that was originally there.
The proponent of the GB theory agrees with earlier theorists that only transitive verbs have passive forms (Black, 1999, p.31). Therefore, no lexical rule can generate a passive form from intransitive verbs. Lexical rules normally help in illustrating generalizations such as this one about the relationship between passive forms and transitive verbs. In a sentence like; John was invited to the party by Jane, a rule like this one below can help illustrate the generalizations.
V [+pass], [_ NP X (PP [to]) (PP[by]) ]
Theme Goal Agent
Sometimes, there is the need for interchanging the subject and object positions. This is possible especially when the subject position has no semantic role at the D-structure and has no lexicon to fill it (Black, 1999, p.32). This agrees with the Principle of No Loss of Information. Normally, a trace remains behind to retain the link between the object and the related semantic role (1999, p.32).
Unaccusative Clauses
There is the need to distinguish between categories of intransitive verbs. To do this, it is important to determine whether the noun phrase in the position of the subject does the action or the action affects it (Black, 1999, p.32).
John feels good.
Jean collapsed.
The plate broke.
John broke the handle.
In the first example above, feels is an ordinary intransitive verb whose subject, John, is an Agent. On the other hand, John just collapsed. He did not do anything to make himself collapse. Therefore, in the second example, the subject has the role of the theme. In the third and fourth examples, the breaking affects “the plate” and “the handle”. “The plate” and “the handle” take the theme role. In the third example, the action is unaccusative while, in the fourth, it is transitive. The verb “Feels” has an Agent in the position of the subject, while “collapse” has nothing in this position but has a theme object and “break” has an agent that is optional.
Raising constructions
This category involves verbs that have a finite or non-finite complement, but do not give semantic roles to their normative positions (Black, 1999). Raising verbs include likely and seem (1999, p.33). The use of the pronoun “it” shows the lack of semantic roles especially in cases when a complement that is finite is in use. In cases where a complement that is non-finite is present, the subject of the dependent clause takes the position of the independent clause.
Conclusion
The most important part of this topic is the meaning of the various semantic roles; agent, source, goal, theme etc. The other thing is to know the rules that guide the movement of lexical items from one position to the other. It is important to know that there should be no cross linking of semantic roles and syntactic categories in related forms.
This topic also stresses that an item is free to move out of a position, but the position should not be filled by another item. This helps avert the problem of altering the semantic role of that position. The semantic roles discussed should be used to bring out the similarities between active and passive constructions.
This work also reveals that the noun phrase occupying the subject position does not have to be doing an action. Sometimes the action of the verb affects it. The NP can, therefore, be an agent or the theme.
References
Black, C. A. (1999). A step-by-step introduction to the Government and Binding theory of syntax. Summer Institute of Linguistics-Mexico Branch and University of North Dakota. www. sil. Org/americas/mexico/ling/E002-IntroGB. Pdf.
Dang, H. T., & Palmer, M. (2005, June). The role of semantic roles in disambiguating verb senses. In Proceedings of the 43rd Annual Meeting on Association for Computational Linguistics (pp. 42-49). Association for Computational Linguistics.
Gildea, D., & Jurafsky, D. (2002). Automatic labeling of semantic roles. Computational linguistics, 28(3), 245-288.