Hi everyone,
I have here a sentence and am not sure why it is in inthe present perfect tense and not past tense.
Environmental laws make the new owner liable for toxic chemicals that may HAVE BEEN LEFT BEHIND on the property 50 years ago.
Why not “that may left behind” doesn´t “ago” indicate a simple past tense?
No, that won’t work, I’m afraid,
You’re right in saying that “ago” refers to a past event.
But the construction “may have been left behind” is used to indicate a possibility that something happened in the past, it is NOT a statement of fact.
He may have been here - there’s a possibility that he was there, but I don’t know for sure.
Thanks a lot
“that may left behind” is ungrammatical – irrespective of “ago” or anything else in the sentence.
In my humble opinion
“Have been left” here isn’t a present perfect but
“may have been left” is a perfect conditional.
may ~ a modal
have ~ the first auxiliary
been ~ the second auxiliary used for passive voice
left ~ main verb
Modal + have as the first auxiliary + main verb ~ perfect conditional, active voice
Modal + have as the first auxiliary + past participle of the verb to be + main verb ~ perfect conditional, passive voice
This form can be made using another modals
I could have done this
I must have done this
etc
Different modal determines different meaning of the form (perfect conditional) and the complete sentence of course.
I’ve just said how I, as a learner, see the form.
I know grammarians would say that “may” is a verb here, it means the first auxiliary.
Thanks
you are totally right that it is a perfect conditional.
How could i forget it …
Thx for helping
You guys are great 
You’re welcome! Now I have a question
“How could I forget” or “How could I have forgotten”?
And of course we do not use all the modals to make the perfect conditional. (will/shall for example)
Thanks
If i am not mistaken its “How could i forget it”
Both are correct. It depends on which tense you need to use for the particular situation.