Positive

Negative

Fact:

I know

It is cold in that house.

It isn’t cold in that house.

Deduction:

I'm sure

It must be cold in that house.

It can't be cold in that house.

Deduction:

It's possible

It might be cold in that house.

It might not be cold in that house.

It could be cold in that house.

Don't use couldn't

It may be cold in that house.

It may not be cold in that house.

Deductions about what is happening now:   
be ___ing:      She's not answering the phone. She might be sleeping.