Implicit arguments are arguments that occur in Logical Form, but are omitted in the syntax. Consider the following sentences:
(1) Mary was run over by a car.
(2) Mary was run over with a car.
(21) implies that there is no perceivable or known agent. The car could have slipped its brakes. There is no perceivable agent. (22) implies that there is an agent, but the agent is not expressed. Either the speaker does not know who the agent is or he does not wish to divulge the identity of the agent.
The dummy verb by does not directly mark agency, since car is an instrument in (21) as well as (22), and it occurs in construction with an experiencer as in:
(3) Mary is liked by John.
By is inserted to assign Case to the highest argument in the theta role hierarchy. The hierarchy is expanded now to:
(4) agent > instrument > theme.
If agent is present in the passive, by is inserted to assign Case to the NP assigned the agent. The dummy preposition with is inserted to assign Case to the NP assigned the instrument. These two dummy preposition can only mark secondary complements. If agent is not an argument, then by is inserted to assign Case to the NP marking the next highest theta-role in the hierarchy: the instrument:
(5) The tree was blown over by the wind.
Here wind is an instrument since wind has no CPU. The wind is something that cannot normally be used by humans as an instrument. Note the oddness of:
(6) ?The highway construction workers blew the cars off the road with the wind.
The wind can be an instrument in legendary settings:
(7) To vent their anger the gods blew the blew the illicit apples across the fields with the wind.
This implies that the gods have the power to use the wind as an instrument.
Now let us return to sentence (20). Let's add an instrument:
(8) The potato was eaten with a fork.
(9) *The potato was eaten by a fork.
An agent is implied in (8). The verb eat always implies an agent, and the agent must be animate. Hence, (9) fails since fork is inanimate and it is marked with by which means it must be interpreted as an agent.
Thus, with some verbs speakers are forced to imply the agent though they can fail to mark it in the grammar. In other verbs, they are not forced to do so. The agent may or may not be implied. The use of the dummy prepositions by and with make this distinction.
The arguments that are implicitly understood but not overtly expressed. The implicit nature of these arguments play a role in the grammar of language.
The problem that we now encounter is how to formally represent this.This is a grammatical problem as the use of dummy prepositions indicate. In Logical Form (Propositional Form) the argument <agent: [NULL]> must be present if the verb is eat, drink, stir, write and other similar animate only agent verbs. It is optional for other verbs where an agent is not perceived as necessary for the event to occur: hit, run over, breeze, cook (the heat cooked the egg on the sidewalk), boil, blow. The difference seems to be whether the instrument is a machine (agent optional) or an implement not classified as a machine: knife, spoon, string, flour,honey:
(10) The salami was cut with (*by) a knife.
(11) The soup was stirred with (*by) a spoon.
(12) The packed was tied up with (*by) some string.
(13) The stew was thickened with (*by) some flour. (intentional)
(14) The tea was sweetened with (*by) some honey. (intentional)
Flour and string could be used in agentless constructions where the event is accidental (as opposed to intentional):
(15) The stew was thickened by the flour when the flour bag tipped over.
(16) The tea was sweetened by the honey when the earthquake knocked the honey off the shelf causing the honey to fall into the pot of tea.
We might find a similar kind of reading for cut by a knife, but not *sliced by a knife. It is very hard to imagine how soup could be accidentally stirred by a spoon or a packed accidentally tied up by some string. Thus, the distinction is not in machinery, but in intention. Intention requires an agent whether or not overt. But accidence does not necessarily imply an animate agent.
Let's start with the E-propositional structure of (10):
(17) CUT <patient: SALAMI> <instrument: KNIFE> <agent: [NULL]>.
(18) Definition: [NULL]
(19) [NULL] refers to an argument that is implicitly understood in the grammar but unidentified by the speaker (or writer).
In (5), the tree was blown over by the wind, there is no implicit agent:
(20) BLOW OVER <theme: TREE> <instrument: WIND>.
One problem that we must deal with is the insertion of the dummy prepositions. The use of with implies an agent. The argument is not formally deleted. It receives a null phonetic representation. If <agent:[NULL]> is present, then the instrument must be marked by with, if <agent:[NULL]> is not present the instrument is marked by by.
Another problem is to account in the grammar which arguments can be implicit and which ones cannot.
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