"why do you think..."/"how do you know...": difference in interpretation

[Curt Jugg]

I am having trouble with the analysis of these two sentences:

(1) "Why do you think he stole the money?"

(2) "How do you know he stole the money?"

Superficially they have the same structure, but (1) is ambiguous in a way that (2) doesn't appear to be. (1) can mean either (1a) "Why do you think it was him who stole the money?" or (1b) "Why did he steal the money, do you think?"

If we apply the same reasoning to (2) then it ought to mean either (2a) “How do you know it was him who stole the money” or (2b) “How did he steal the money, do you know?” But it doesn't; (2) is not ambiguous and can only be interpreted as (2a).

Can anyone explain why there is this difference, please?

[5jj]

You are trying to compare two different things. You have less of a problem if you start with:

1. Why do you think he stole the money?
2. How do you think he stole the money?

#1 can be interpreted as:
a. Why is it that you think that he stole the money?
b. Why did he steal the money, do you think?

#2 can be interpreted as:
a. How is it that you think that he stole the money? (admittedly very unlikely, but possible)
b. How did he steal the money, do you think?

Now move on to:
3. Why do you know he stole the money?
4. How do you know he stole the money?

Neither is ambiguous - only one interpretation is possible. Admittedly, #3 is very unlikely, but it's just about possible.

[Curt Jugg]

Thanks very much for your reply. Are you saying, then, that the cause of the ambiguity is to be found in the different meanings of think and know?

[5jj]

Thanks very much for your reply. Are you saying, then, that the cause of the ambiguity is to be found in the different meanings of think and know?

I am saying that the cause of your analysis problem was the different meanings of think and know.

If you compare the 'how' and 'why' questions with 'think', there is no problem. Similarly, if you compare the 'how' and 'why questions with 'know', there is no problem. The problem only arises when you compare a 'why+think' question with a 'how+know' one. There is actually no reason why different verbs should act in similar ways.