Use of Can vs Will

[siclarke]

The doctor thinks the baby can walk in about three weeks.

I know this should be the doctor thinks the baby will walk in three weeks but can't explain / find out why?

Can anyone help?

Thanks

[MrPedantic]

Hello Si

"Can" suggests a present capacity for walking:

1. I can swim = I am able to swim now.

And "will walk" doesn't exclude the possibility that the baby can walk now. Cf.

2. I will walk to work tomorrow.

— here, it's possible that I walked to work today as well.

But in your example, we want to suggest a capacity for walking that does not exist at the moment. So this construction might be best:

3. The baby will be able to walk in three weeks' time.

MrP

[curious]

Mr P is everywhere. Nice to see you here too.

can't "can" express future ability too? So I think

The doctor thinks the baby can walk in three weeks.

should be an acceptable sentence too. Am I wrong?

[Johan[@CLT]]

Hi Curious,

I don't think that "The doctor thinks the baby can walk in three weeks" is wrong but to my mind there might be a better alternative.

First of all, the sentence starts with "the doctor thinks" so it is a possibility then, the doctor isn't sure himself.

The doctor thinks that the baby might walk in three weeks. So, it is a possibility or likelihood in the future.

can is getting used for more general or theoretical kind of possibility and not about the chances that something will actually happen or is happening. phew

Kind Regards

[MrPedantic]

Mr P is everywhere. Nice to see you here too.
can't "can" express future ability too? So I think
The doctor thinks the baby can walk in three weeks.
should be an acceptable sentence too. Am I wrong?

Thank you, Curious! Nice to see you too.

I would say that where a physical ability doesn't exist at the time of speaking, but might in the future, we have to use "will be able to" instead of "can":

1. I can swim! ] fine.
2. ?I can't swim at the moment, but I'm taking lessons next week, and after that I can swim ] unidiomatic.
3. I can't swim at the moment, but I'm taking lessons next week, and after that I'll be able to swim. ] fine.

We can use "can" where something has been planned in the present, however:

4. We can go to your mother's tomorrow, if you like.

Or to mean "may" for a future event:

5. You can use my car next week, if you want to. I won't be needing it.

But cf. this version, which expresses ability, rather than permission:

6. You'll be able to use my car next week. I won't be needing it.

MrP

[curious]

thank you.