Definition of "infinitival"

For example, we want to be able to stipulate in the lexical entry for persuade simply that it takes an NP and a clausal Complement ([...]). From the meaning of persuade, it will follow that the clausal Complement cannot be interrogative or exclamative. From independent word-order restrictions (an NP Complement must be positioned immediately adjacent to its sister V), it will follow that an NP Complement must precede the clausal Complement. Given that both Exceptional Clauses and Small Clauses must immediately follow a transitive Verb, it will follow that the clausal Complement of persuade cannot be an S or an SC, but rather must be an S-bar. Given that S-bar can be either finite or infinitival, we should expect to find that in the unmarked case, either type of clausal Complement is possible with persuade: and examples such as the following suggest that this is correct: (64) (a) Mary persuaded John [Sʼ [C that] he should resign] (64) (b) Mary persuaded John [Sʼ [C e] PRO to resign]

1988, Andrew Radford, chapter 7, in Transformational grammar: a first course, Cambridge, UK: Cambridge University Press, page 360