What's the difference between in 10 years and for 10 years?

Question

1. We haven't spoken in ten years.
2. We haven't spoken for ten years.

What's the difference between the two in meaning?

Answer 1

You have an interesting example! In your example the meaning of the two are equivalent, but that's not usually the case.

Normally

When we say in 10 years we mean that something will happen in the future (the time that will elapse before the event).

When we say for 10 years we mean that a situation has been happening (or will be happening with a future verb) over a period of 10 years (duration of time)

In your example

Your first option "We haven't spoken in 10 years" is using in to refer to a period of time during which the situation has continued. This is because the verb is in the past and refers to an ongoing situation (not speaking) and then in gives the amount of time that has elapsed since that situation first started. So because the event is the star of an ongoing situation in this case the effective meaning is the same.

Answer 2

We haven't spoken in ten years

we haven't spoken for ten years

The question has been asked on different sites.Nobody could differentiate between the two sentences.

I think both have the same meaning and are grammatically correct.