[Grammar] can/could

[Mathilde.]

For an essay, I'm trying to express the idea that protocells - which may have appeared 4 billions years ago but don't exist anymore - were not able to do something (we are very sure of that).

My sentence is for now : "However, these constructions cannot have permit metabolism andreproduction."

I'm struggling with cannot/couldn't : Can isn't more final ? Or do I have to use could with the past tense ?

 

[Tarheel]

Perhaps:

Those organisms could not reproduce.

They sure couldn't have been around very long, could they?

(Say four billion years.)

 

[Tarheel]

Say:

Isn't "can" more final?

Neither is more final. (There are not degrees of finality.)

 

[emsr2d2]

For an essay, I'm trying to express the idea that protocells - which may have appeared 4 billions years ago but don't exist anymore - were not able to do something (we are very sure of that).

At the moment, my sentence is "However, these constructions cannot have permit metabolism and space here reproduction."

I'm struggling with "cannot/couldn't". Is "cannot" [STRIKE]isn't[/STRIKE] more final no question mark here or do I have to use "could" with the past tense?

As has already been noted, "cannot have permit metabolism and reproduction" makes no sense. Is "permit" there meant to be a noun attached to "metabolism" or a verb? If it's a noun, I don't know what "permit metabolism" is. If it's a verb, you need either "cannot have permitted" or "couldn't have permitted".

 

[Mathilde.]

Thank you all !

Actually, they probably sticked around a bit. I think that's the subtlety : they weren't living organism so they didn't need to reproduce. However, as a part of a theory on "how life on Eart began", the scientist needed them to be able to reproduce, and they weren't (at all, under no circumstances), and so the theory had been discarded.

That's the meaning I'm trying to convey with the sentence. Maybe this one is better :

However, these constructions couldn't have given rise to metabolism and reproduction fonctions.

 

[Tarheel]

Thank you all !

Actually, they probably stuck around a bit. I think that's the subtlety : they weren't living organisms, so they didn't need to reproduce. However, as a part of a theory on "how life on Earth began", the scientists needed them to be able to reproduce, and they didn't (at all, under any circumstances), and so the theory was discarded.

That's the meaning I'm trying to convey with the sentence. Maybe this one is better :

However, these organisms couldn't have given rise to metabolic and reproductive functions.

You might be right.