"I understand you" vs "I do understand you" [duplicate]
Possible Duplicate:
What is the difference in meaning between “I play” and “I do play”?
What is the difference between "I understand you" and "I do understand you", and what kind of grammatical structure is the last one?
Solution 1:
The second is simply more emphatic than the first. Its structure has been called the emphatic present:
The emphatic present: The present tense can be expressed with emphasis by using the auxiliary verb do and the uninflected main verb: (I do walk, He does walk).
The extra "do" is used when the speaker wishes to express that s/he really means it:
I don't think you understand me.
Yes I do understand!
It wouldn't sound as natural for the second speaker to say Yes I understand! in that scenario instead.
Solution 2:
I think calling one construction more 'emphatic' than the other is a bit misleading. Their emphasis is very different. "I do understand you" is used when there might be significant reason for the listener to believe that the speaker does not understand, and the speaker has noticed this potential source of confusion, and wishes to emphasise that this is not the case. Its most common uses are:
When the listener makes some direct hint (subtle or otherwise) that they believe the speaker might not understand, e.g. in response to "you just don't get it, do you?".
When the speaker is about to say something that they believe might cause the listener to think they have misunderstood, e.g. as a prefix to a contentious statement.