Nonfinite clauses tend to express less information than matching finite clauses
by to or
–I want [to buy
–[To err] is
–[For him to
err] is terrible.
also appear without to:
–I heard him
break the cookie jar.
–He made me eat
be nominal, adverbial (I bought
it [to surprise you].), or adjectival (He was the last person
She feels sick.
I was watching TV.
In the first example, we have the present tense verb form feels. We could change to past tense: She felt sick.
In the second example, the verb phrase was watching contains the past tense form was. We could change to the present tense: I am watching TV.
These are called finite clauses because they contain finite verbs: verbs in the present tense or past tense form.