'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?
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.