[i] She was the only one to talk to him. (Tr = Tm)
[ii] She was looking for someone to talk to. (Tr > Tm) * Tr:Time referred to, Tm: matrix time
Temporal location is closely bound up with modality: the infinitival commonly conveys non-actuality, which tends to be associated with posteriority. The temporal difference between [i] and [ii] thus correlates with the difference in modality: in [i] the talking is actual, whereas in [ii] it is potential.
(The Cambridge Grammar of the English Language, p162)
I guess the book says only has the modality in [i], by which to infinitival has the meaning of actuality. I can get what it says, but wonder if to talk can be replaced by talking in [i] without semantic change.
In [i], does the word, only, permits just the actual meaning and not the potential one? If this is yes, what about the example below? (a)’s to infinitival must be an actuality. But what about (b)? Its to-infinitival seems like potentiality with only in the sentence. In this case, left seems to make the sense. Is this right?
(a) They were the only people to survive the crash.
(b) The only thing left for us to do is wait. (Merriam-Webster’s)