# Theta Criterion

## Definition

Theta Criterion is a condition which states that at D-structure each argument is in a theta-position, and that each theta-position contains an argument. If the theta-criterion is defined over LF it says that each theta-position is in a unique chain, and that each chain contains a unique theta-position.

## Examples

The theta-criterion accounts for the contrasts in (i) and (ii).

```(i)   a   it seems that John is ill
b  *Bill seems that John is ill
(ii)  a	  Bill believes that John is ill
b	 *it believes that John is ill
```

In (i)b the argument Bill is in a theta-bar position; in (ii)b the expletive it (a non-argument) is in a theta-position. Originally, the theta-criterion stipulated a unique relationship between arguments and theta-roles (rather than theta-positions), forcing the analysis in (iii)b on John left angry: unless angry brings its own (PRO) argument, there would be two theta-roles (assigned by left and angry, respectively) for one argument (John). Revising the theta-criterion in terms of theta-positions allows the analysis in (iii)a where the unique argument John is in a unique theta-position associated with two theta-roles.

```(iii) a	 John left angry
b	 John left [PRO angry]
```

In Brody (1993) it is argued that the theta-criterion can be dispensed with.