Do these sentences have the same meaning: "I don't think he is a student." and "I think he is not a student."

Question

1-"I don't think he is student."

2- "I think he is not a student."

The speaker has the opinion that "he is not a student". But in order to say this in English, we make up the sentence like this ""I don't think he is student."

Because I am not a native speaker, from my logical point of view, both sentences seem to give the same meaning". Either way, the speaker has the same opinion about him, which is "He is not a student".

And what is interesting is that this structure is true for these types of sentences that start with "I think, I suppose, etc". These parts of sentences turn into "I don't think...., I don't suppose ...." to make it negative, whereas the negative situation is actually in the second sentence -not in the first one.

So I wonder why can't we form such sentences like this: "I think he is not a student." Why do we really have to make the first part negative in such sentences, whereas the situation in the second part is actually my opinion.

And I really wonder, what would it sound like if sentences starting with "I think, I suppose, etc" were formed the other way around? Would it be a small mistake or completely unacceptable?

Answer 1

Both of the sentences

I don't think he is a student.
I think he is not a student

mean the same. Note I have inserted the a in the first one which you had left out. The first form is more frequent and sounds more natural but the second form is perfectly useable.

Answer 2

The two versions usually have the same meaning, but not necessarily. For example, let's say that you're on a jury. The foreperson believes that a consensus has been reached and tells the jurors, "We all agree that the defendant is guilty, right? In that case, I'll tell the judge that we've reached a verdict." You might respond:

Wait, I don't think that he's guilty! <-- You might believe that the defendant is innocent, but you might simply be unsure and want to deliberate further.

or

Wait, I think that he's not guilty! <-- Your belief is clear.

That being said, the second version is usually avoided in favor of the first, which is often understood to have the same meaning as the second. You can certainly use the second--it is entirely correct--but it may sound somewhat unnatural to native speakers. Exactly how unnatural would depend on the actual text and context. (The second version would be more common in my example, because "not guilty" is a common phrase in English.)