'are believed' indicates the passive voice, to me, and the 'have developed' the present perfect.
I am not sure what you are objecting to. I did say the present perfect tense.
Your two last examples are past tense
Are you saying the OPs example is not a perfect tense? The present simple tense would be 'We believe that land animals develop from sea animals'.
Edited by: billybart
#10 -- What I'm saying is that your statements
The present perfect tense describes something from the past which is still current or relevant or has an effect on the present.
The belief originated in the past and is still a current belief.
imply that the fact that the belief originated in the past and is still a current belief has something to do with the occurence of the present perfect "have developed" in OP's example. It doesn't. The fact that the belief is a current belief is reflected in the tense (present) of the passive verb "are believed." If the belief were no longer a current belief, you would use "were believed." If it were relevant that the belief originated int eh past and was still current, you would have a sentence like this:
Whales have long been believed to have developed from land animals.
The present simple tense would be 'We believe that land animals develop from sea animals'
You're mixing up tense and voice. "are believed" is present simple, so is "we believe". The first is passive, the second is passive. For past passives and present perfect passives, see #11.
We will have to agree to disagree on this, but I think that you should read up on perfect tenses.
Not voice.
Present Perfect With verbs of state that begin in the past and lead up to and include the present
To express habitual or continued action
With events occuring at an indefinited or unspecified time in the past -- with ever, never, before
He has lived here for many years.
He has worn glasses all his life.
Have you ever been to Tokyo before?
Yes, but have you read it? 'have developed'
