Hello people. I have a question about passive form.
I've thought if subject can't do somethig by itself or something causes subject to do something, passive form will be used. But, I came across quite tricky sentence which doesn't have passive form even subject seems can't do something by itself.
I'll give you example first which is not passive below.
"Our universe could have formed out of the quantum foam of two parent universes."
In the above sentence, in my opinion, it seems like the thing could have formed 'our universe(subject)' is 'quantum foam of two parent universes'. Incidentally, the sentence don't have passive form.
Is it okay not to use "Our universe could have been formed out of..." rather than "Our universe could have..."?
The word 'form(ed)' in your sentence above is an 'intransitive' verb meaning 'to start to exist and develop.'
form - Definition and pronunciation | Oxford Advanced Learners Dictionary at OxfordLearnersDictionaries.com