Projection and Theta-Marking

What are Thematic Relations? Answer: The relations the participants of the action (or more generally) situation described by the predicate bear the to the situation, relations such as being an active agent, being a cause, being the source from which motion or energy begins. Objection: But there are many such relations and each participant bears many of them. How do we know which ones are important?

Why do we introduce Theta-roles? Answer: It turns out that the notion of a thematic relation, while useful, is raises many issues we do not need to deal with as syntacticians. What we really care about is not what the exact thematic relations are or how many of them there are, but just that fact that there is a unique cluster of relations for each argument. We call that cluster of relations that makes each participant different from the others the participants theta-role. Thus the claim is not that there is a unique relation chosen from some special set that each participant bears but that there is a set of relations uniquely identifying each participant.

Even when we have a verb where two participants seem to be doing the same thing, there always turns out to be some subtle difference on closer inspection:

1. The car collided with the truck.
2. The car and the truck collided. (paraphrases [1], car and truck bear same thematic roles?)
3. The car collided with the lamp post.
4. ? The car and the lamp post collided. (does not paraphrase [3])

The following principle formalizes this idea.

Theta Criterion


Each argument bears one and only one theta role, and each theta role is assigned to only one argument.

And here is the principle we will use to hook this idea up to the syntax:

Projection Principle


Syntactic Representations must be projected from the lexicon, in that they observe the lexical properties of the items they contain.

The things we have been doing can be viewed as ways of implementing of these principles

1. Theta-grids are determined (or at least constrained) by semantic properties.(Theta criterion)
2. Verbs must enter trees compatible with their theta grids (Projection P)

This leaves one more principle

Extended Projection Principle


Clauses must have subjects.