Help Me, Philosophic Types

I want to make an argument that there is a fundamental difference between "Critical" and "Dialectic" methods of thought. I do not think that my arguement is stretching anything. However, I have attempted to make this argument to others and been questioned on this basic distinction. I am seeking confirmation of my sanity.

I understand the Modern Critical Method as taking nothing for granted: its goal is to show that X is not the case, to question the very nature, existence and truth claim of X, and in some cases to go on to explain how the idea or belief in X came about. Classical Dialectic, on the other hand, while its method is necessarily negative, starts from the existence of X. Socrates in the dialogues of Plato, does not ever question that X is. Where is the discussion on whether or not there is "good"? Whether or not X or Y or Z is good is discussed throughout, but the existence of the Good is not in doubt; the same could be said for the Beautiful or the Just. I think this is so basic that it is the fundamental basis of the Dialogues. The "Elenchus" is useless unless there is a point of Catholic Truth (not in the religious sense). There is a difference between Plato and Descartes (to use him as representative).

I see a parallel between this (Dialectic) and Apophaticism. Negation is the method, but at the heart of it there is unquestioned reality. Imperfect language can only be used negatively to refer to the real being/notbeing. The Being/Notbeing is not questioned.

I need to learn to write with fewer qualifying clauses. I've been reading too much Thucydides.