Most human languages are transmitted by sounds and one of the most obvious differences between languages is that they sound di

Semantic roles and grammatical relations 
In a sentence like The farmer is killing the ducklings, there is a difference in the 
relationship between the two noun phrases and the verb — we know that the farmer did 
the killing, and the ducklings ended up dead, and we could talk about them as the ‘killer’ 
and the ‘thing-killed’. But we know that these are quite similar semantically to the 
‘hitter’ and the ‘thing-hit’ in The farmer is hitting the ducklings. For this reason, more 
general terms are used to express the semantic role (also called the theta role) which a 
noun phrase plays in a sentence. Different systems of semantic roles are used, but some 
of the more common terms are agent (the one who performs something, as the farmer 
above), patient (the one to whom things happen, the ducklings above), experiencer and 
theme (I and him respectively in I saw him, where I do not really do anything, and 
nothing actually happens to him), recipient, and source and goal (where something 

---

33 
comes from or goes to respectively, as house and shops in she left the house for the 
shops). 
Semantic roles are needed to talk about sentence construction. For example, in English, 
if a transitive verb has an agent and a patient, the agent comes before the verb and the 
patient after, which is how we know who does what in The farmer is killing the 
ducklings. If the sentence is made passive (The ducklings are being killed by the farmer), 
then as well as a change in the verb, the patient now comes before the verb, and the agent 
is either in a prepositional phrase with by, or omitted entirely. 
On the other hand, we clearly need more than just semantic roles in language 
descriptions. In the sentences The farmer is killing the ducklings, The ducklings are 
being killed and I saw him, there is something in common between the first noun phrase 
of each sentence, even though they are respectively agent, patient and experiencer. This 
noun phrase comes before the verb; if the verb is present tense it controls the form of the 
verb (e.g., is versus are); and if the noun phrase consists of a pronoun it has nominative 
form (I rather than me). For this reason we need grammatical relations such as subject,