Absolutely you can. By holding onto an implicit concept of "that which is good", one is able to determine what is not good, due to its inconsistencies of the preconceived notion of "that which is good". I'll use here an example of aesthetics.
Person A: Gee, that sunset is beautiful
Person B: No, that sunset is not beautiful
Person B did not have to conceive of ugliness to arrive at that conclusion. He merely had to have a preconceived notion of "that which is beauty" of which, the sunset was not in accordance with.
Thus, it is the preconceived notion of the fullness of beauty that provides the measuring stick of all aesthetically claims and allows for human predication. In the same way it is the fullness of truth, good etc. that allows for predication of all epistemological or ethical claims.
Negative is the absence of positive, in the same way darkness is the absence of light. It holds no ontological existence on its own.