Reason is negative and dialectical because it resolves determinations of understanding into nothing; it is positive because it generates the universal and comprehends the particular therein. Hegel, Science of Logic, 28/1: 16
What does this mean? Here's how I see it: reason lacks any prominent characteristics and is subjective, consisting of contradictions. To be honest this is as far as I've got. I have never really dabbled in philosophy, so if the answer was kept simple, I suppose that would make it easer for me to understand.