In stead of thinking of thhe words as containers of meanings we can look at the roles they perform within the sittuation described by a sentence.If the situation is a simple event ,such as "The boy kicked the ball"then the verb describes an action(kick).The noun phrases describe the roles of entities,such aspeople and things,involvedin the action.We can identify a small numberof semantic roles for these noun phrases.
Agent,theme,instrument
In the sentence above ,one role is taken by the "boy"as the entity that performs the action techincally known as"agent".Another role is taken by the "ball" as the entity is involved in or affected by the action technically known as "theme".The theme can also be an entitythat is simply being dscribed as in the "The ball was red".Identifying entities denoted by the noun phrases as the agent or the theme is a way of reconising the semantic roles of those noun phrases in a sentence.
Although agents are typically human,they can also be non-human forces(the wind blew the ball away),machines(the car ran over the ball),or creatures(the dog caught the ball).If an gent uses another entityin performing an action,that other entity fills the role of instrument.In writing with a pen or eating with a spoon,these noun phrases have the semantic role of instrument.
Experiencer,location,source,goal
When a noun phrasedesignates an entityas the person who has a feeling,a perception,or a state,it fills the rol of experiencer.If you see,know or enjoysomething,you donot really have to perform any action(hence you are not the agent).You are in the role of experiencer,If someone asks"Did you hear that noise?",the experiencer is you and the theme is that noise.
A numberof other semantic roles designate where an entity is in the description of the event.Where an entityis(on the table,in the room)fills the role of location.Wherean entity moves from is the source and wher it moves to is the goal.When we talk about transferring moneyfrom savingsto checking,the source is savings and the goal is checking,All these sematic roles are illustrated in the following scenario
Mary saw amosquito onthewall
experiecer theme location
She borrowed amagazine from George
agent theme source
and she hit thebug with the magazine
agent theme instrument
She handed themagazine back toGeorge
agent theme goal