This =! Not something else

Consider this sentence – A gave a ball to B.

And consider this question – why did he give a ball to B?

Now there are 2 possible kinds of interpretations of this question – 

1) Why this? – 

Why did he give a ball to B?

2) Why not something else? – 

Why did A give a ball to B?

Why did A give a ball to B?

Why did A give a ball to B?

The above 2 sets arent equivalent to each other. The first set (first question) is not equivalent to any of the other 3 (in the second set). (In the first set, none of the 3 i.e. A, ball and B, is more important than the other 2. All the 3 words are equally important, unlike the 3 questions in the second set).

This shows that ‘THIS’ is not the same as ‘NOT SOMETHING ELSE’ !