Empty infinitive?

Is there a grammatical term for the reduced infinitive form "to" in sentences like the following?

<No, but I'm planning *to*.>

<I haven't done so yet, but I want *to*.>

I've never read anything about it, but I noticed it on my own a while ago and I've always conceived of it as an "empty infinitive".

???

I read one more term for the same purpose which was used in one of Barrons TOEFL books. That is, "bare infinitive".

It's good old-fashioned ellipsis which allows English to drop words but still achieve lingusitic closure.

Typo!

That should have been "linguistic."

By the way, "bare infinitive" is a thoroughly spurious term used by certain "grammarians" to refer to the infinitive when it is not preceded by the prepositional marker "to."

The thing that seems important here is that appears that "to" has become actually more tightly bound to the verb that precedes it than the infinitive that it supposedly marks, if not actually directly incorporated into the preceding verb, as it seems to have been in cases like "have to". This is further implied by how people speak of things like "have to", "need to", "be supposed to", "be used to", and like as if they were coherent units themselves of which the "to" is an integral part, rather than having "to" just act as a mere infinitive marker. Consequently, I would almost favor an analysis where "to" is no longer part of the main verb at all, but rather is part of such quasimodal constructions themselves.

I'd agree. It's similar in some ways to certain French verb constructions that demand "à" before an infinitive.