I think/ I believe

[ruofei]

Dear teachers,
'I think' and 'I believe' can sometimes be used in a similar way, but can't always be interchangeable, can they?
Could you explain to me what is the difference please?
Many thanks,
Ruofei.

[Tdol]

I believe'' can be used to mean 'I think':

I believe he'll be there = my idea/opinion

It also has a different meaning of 'accepting something as true':
He said he was ill and I believe him.- You could not use 'think' here, nor in 'I believe in God'.

[aaa]

As far as I know, there is at least one case that differs 'I know' from 'I believe'

believe in smth. or doing something = think something is reasonable, worth and so on.

For instance: I don't believe in tips or I believe in spending time in such way

Correct me if I wrong :)

[ruofei]

[...] or I believe in spending time in such way

What do you mean by that?

Actually, one of my students came up with this sentence: "I'm tired, I believe I'll go to bed soon". And I felt it just didn't sound good. Yet, I couldn't clearly explain to her why she should have said: "I think I'll..."
Now, thanks to Tdol's clarification, I know that nothing is to be taken as a true so she can't use "I believe" in this context.

[Tdol]

That example doesn't make much sense to me either.