syntactic analysis - How to parse the grammar of a sentence that appears to have two tensed verbs

This question came from a student of mine - he wanted to know how to parse the grammar of this sentence, which appears to be simple but clearly is not:

• Peter seems to have found his glasses.

Sentences of this form are very common in English but the syntax is puzzling. The main verb is clearly seems, usually a link verb, so the basic syntax ought to be:

Subject + Link Verb + Subject Complement S+LV+SC

But the verb phrase to have found appears to be tensed (present perfect), and the meaning delivered is similar to the the tensed form (he found them and they are still found). But this verb phrase can not be tensed and does not agree with the subject (if it did it would be has found). It has to be a verb complement.

Now, the rule for subject complements is generally that they are either an adjective phrase or a noun phrase, but this complement is neither, and yet it clearly is describing the subject.

So the question is - how do we parse this?

Other sentences with the same form follow:

• The answers given seem to have addressed your question adequately.


• I am lucky to have found this site.


• The library seems to have closed.

So, what is the best way to parse the grammar of sentences like these?

Answer

How to parse the sentence is not simple. First, it is not a simple sentence. It has two clauses, each with a main verb. The matrix verb is seem, and it is tensed. The rest of the sentence is part of the subordinate infinitive clause, whose main verb is find. But infinitives don't have tense, so it is not a tensed verb.

The logical structure of the actual sentence is something like

• *seem* (PAST (*find* (*Peter*, *his glasses*)))

which means, roughly that some past event of Peter finding his glasses appears (to the speaker) to have happened. That is, the infinitive clause

• (for Peter) to have found his glasses

is the subject of the verb seem. English does not allow that construction, however:

• *For Peter to have found his glasses seems.

Instead, English requires either the rule of Extraposition, which puts in a dummy it as subject, and requires a that-clause:

• It seems that Peter has found his glasses.

Or it requires the rule of Subject-Raising, which has applied here, moving Peter, the subject of the subordinate clause, up to become the supposed subject of seem:

• Peter seems to have found his glasses.

Raising requires an infinitive complement, which is of course not tensed.