Definition of "nonfinite"

Although a finite I ( = INFL = INFLECTION) constituent is (overtly or covertly) inflected for TENSE or AGREEMENT properties, it should be obvious that a nonfinite I in English lacks these properties. Hence, the infinitival particle to which occurs in a nonfinite I is by its very nature tenseless and agreementless (i.e. it carries no Tense or Agreement properties, and is thus an entirely uninflected form). The difference between a finite and a nonfinite Clause can thus be seen to lie in the nature of I: a finite Clause is one which contains a finite I (carrying Tense and Agreement properties); a nonfinite Clause is one which contains a nonfinite I which is tenseless and agreementless.

1988, Andrew Radford, chapter 6, in Transformational grammar: a first course, Cambridge, UK: Cambridge University Press, page 306