To be

[Guest]

Ron/Stacey

I read somewhere that:

1) To be + complement -- points to present tense, (The depletion of ozone layer is believed to be the cause of all problems)

2) To have been --- Points to past tense (The impact of meteorite is believed to have caused the extinction of dinosaurs)

My question is, Believed in # 1 looks past tense but turns out to be present tense and "to have" in #2 looks like present but is past .. Can you please explain the usage of these two structures.. An Analogy for each would be lke "cherry on the cake" :) . thanks in advance

[StaceyKoprince]

I'm sorry it has taken us so long to get to your question.

The depletion (prep. phrase) [is believed] [to be] the cause (prep. phrase)

The impact (prep phrase) [is believed] [to have caused] the extinction (prep. phrase)

You've got two different structures here.

First "is believed" means whatever's comig is something that someone believes right now in the present. That's in both of your examples - no difference there.

Then, you have either "to be the cause" or "to have caused." If you use "to be the cause" you're using the infinitive of the verb to be and then the noun "cause." An infinitive does not give us a tense, by definition; neither does a noun. So this pairs up with the previously provided tense "is believed" and it is the cause today (or at least people believe so).

If you use "to have caused" you've now brought "cause" into verb form instead of noun form. So instead of talking about "the cause" as a noun - which doesn't give us a tense but just follows the tense of the previously given verb - you're now using the past participle "caused." Now we've switched to talking about something that was causED - in the past.