grammar problem

[lisa***]

good day everyone!

we say " i don't think so"and " i think so"
but we say " i hope not" and " i hope so"
not "i don't hope so."
and why not " i think not"

why is that?
i was asked why but couldn't find an explanation.
please help me.

thank you!

[Mister Micawber]

.
I don't think so is an example of transferred negation (transferred from the dependent clause to the main clause). Only certain verbs are normally subject to transferred negation, and some of these are: think, suppose, believe, expect, feel, seem. Hope is not among them.

We do, however, say I think not, as an isolated emphatic response:

A: Shall we stop in and visit your ex-boyfriend tonight?
B: I think not!
.