Or it isn't because you don't agree with the premises or a conclusion made. Possibly because there is subjective part to it, or because there is really something missing or something wrong. In that case, you don't understand it that you are making an argument that you simply cannot agree to, because the premises or conclusions are wrong, but you clearly seem to believe it is true.
Sorry, MR, but I am not following what you are trying to say here.
"I don't understand X", if true, means that I have no authority to make a claim as to the nature of X. It may also be that I only understand
part of X, so that my ability to make a rational claim about X is limited to the scope of what I understand about X. However, my understanding of any given thing is the absolute limit to which I can know anything about it (and thus, to my ability to make rational statements about it).
So long as one intends to communicate rationally, this is something that simply cannot be gotten around.
Some examples:
1. I understand some parts about how my car works enough to repair them; others I do not. I can offer rational advice only on repairing those parts I understand, and that advice is rational only to the limit of my understanding.
2. If I fail to understand how to use Microsoft Excel, then my ability to rationally make a spreadsheet with Excel is limited solely by my ability to gain understanding (either through training or using the Help fuction). I cannot rationally say that Excel is crap for making spreadsheets unless I understand Excel, after which I can make a rational conclusion as to its effectiveness (which, IMHO, is pretty good).
3. I cannot rationally answer a question related to the "old-schoolness" of GURPS because I don't have sufficient grasp of GURPS, either in the case of rules or of play experience, to have a valuable opinion. If I undertook to understand GURPS more fully, my opinion of GURPS would be as good as -- and no better than -- my understanding of it.
RC