- Hey John, what do you think?
- I think that sucks!
- It doesn't make any sense.
vs.
- Hey John, what do you think?
- I think that sucks!
- You're not making any sense.
What's the difference between these? Are there any emphases in the meaning?
In the first dialogue, the line "It doesn't make any sense" sounds as if it were uttered by a third speaker. Someone is asking for an opinion, and two people give two different answers that refer to the same thing or situation. If this isn't the case, it would sound better if it became "What you're saying doesn't make any sense," or if it were elaborated.
In the second dialogue, "You're not making any sense" is interpreted as "I don't understand what you are saying". It serves the purposes of communication a lot better, as it doesn't create ambiguities, like the first dialogue.
There's a formatting problem here. How many speakers are there and who says what? In the first triad, John could mean "It's terrible because it doesn't make any sense", but the first speaker couldn't be saying the third sentence. What doesn't make any sense, John's "I think that sucks!" response or what the speaker has asked John to comment on? Irene's suggestion that "It doesn't make any sense" sounds as if it might have come from a third speaker is a good one. It does to me too.
In the second triad, The first speaker seems to be making an ad hominem attack on John because "You're not making any sense" is about John and what John says, not about what the first speaker has asked John to comment on, which requires "It doesn't make any sense".
First, the dialog needs to be clearer, which means that the names of the speakers (even if only "A" and "B") must be included. Second, there is no context for the first line that asks "What do you think?" What does John think of what? Maybe the pronoun "that" or "this" is required (minimal context but no change in meaning). To understand why John isn't making any sense, we need to know what he's been asked to comment on and why his "I think that sucks!" response is, apparently, inappropriate.
There is no change in emphasis from the first to the second triad, only a change in focus to from either what John says or what John has been asked to comment on (it) to John himself (you're).
In other words, without more information, this question cannot be satisfactorily answered.
Notwithstanding Bill Franke and Irene's answers, the use of make sense could indicate, like the simple present, 'general time' the focus on the thing being discussed as illogical, regardless of when the speech act is taking place. Whereas is making sense, a progressive or continuous form, could indicate the focus on the speech act, rather than any particular judgement on the topic generally.
If the first and the third lines are uttered by the same person and the second by John, then it is clear that in the first version, the speaker agrees with John by saying that It doesn't make sense (whatever they are talking about), while in the second version, the speaker challenges John by saying that he is not making sense. He is saying to John: "What do you mean by 'that sucks'? How can that suck? You're not making any sense to me!"
