To clarify the circumstances requires more effective measures than have/has been supposed,
I have asked some native speakers of English and interestingly, their answers somehow are contrary. Here are their answers.
The easy answer here is "than have been supposed". I think most speakers would prefer this version. Possibly people might be thinking of a "dummy subject" here: it has been supposed that we need to take more effective measures to clarify the circumstances. To use "has been supposed" in your question seems to require that the speaker refer to an "it" that isn't mentioned in the sentence: To clarify the circumstances requires more effective measures than has been supposed = To clarify the circumstances requires more effective measures than it was supposed earlier we needed.
This thinking is too convoluted and disjointed for me. I agree with you: To clarify the circumstances requires more effective measures than have been supposed.Now I am thoroughly confused. Seems either have or has is acceptable. But I do need your help to make sure which one is the correct answer, in terms of academic knowledge. Thanks.It could go either way, but I personally would only use 'has'. The 'have' can't be agreeing with plural 'measures', because you don't suppose measures. (Nor do you suppose circumstances, though that is better, more plausible.) What has been supposed is that certain measures are required - and to clarify the circumstances requires more than this. It requires more than has been supposed. There is no overt dummy 'it' for the verb to agree with, but this is the meaning: the situation, not the measures, is what is being supposed.
I think "to clarify the circumstances" is the subject. Hence "requires." "To clarify ... requires."
I don't agree with the rest. I would make "have" agree with "measures."
As far as the rest goes, I guess it's a matter of working out who has been supposing, or even if it's active or passive.
It has long been supposed that ...
We have supposed, in the past, that ...
"... more effective measures than ??? been supposed." - Supposed by who? Surely it's not the measures that are doing the supposing? It's people. Up until the point of the article being written, people had supposed that certain measures were required, but now, for some reason, it is clear that more effective measures are required. I still come up with "had".
My brain's starting to hurt!
To clarify the circumstances requires more effective measures than (those which) have been supposed ( by those concerned up to now),
*To clarify the circumstances requires more effective measures than (those which) has been supposed (by those concerned up to now),
I vote for 'have',
There should be a law against ellipsis, death penalty every time!
I would say 'Clarifying the circumstances requires more effective measures than have been supposed.'
'.....than had been supposed.' would also work.