Theta criterion
The theta-criterion (also named θ-criterion) is a constraint on x-bar theory that was first proposed by Noam Chomsky as a rule within the system of principles of the government and binding theory, called theta-theory (θ-theory). As theta-theory is concerned with the distribution and assignment of theta-roles (a.k.a. thematic roles), the theta-criterion describes the specific match between arguments and theta-roles (θ-roles) in logical form (LF): Being a constraint on x-bar theory, the criterion aims to parse out ill-formed sentences. Thus, if the number or categories of arguments in a sentence does not meet the theta-role assigner's requirement in any given sentence, that sentence will be deemed ungrammatical. . In other words, theta-criterion sorts sentences into grammatical and ungrammatical bins based on c-selection and s-selection. (Wikipedia).
