Understanding and Reason in Hegel

Here is Hegel on two basic things he thinks any particular philosophy should be able to explain: understanding and reason. Why pick these two phenomena? First, these are the two most uprooted by Kant, so they have a particularly impending character for any philosopher of his time. Second, these phenomena correspond to quite clear potentials of our existence that we engage in every day: they seem tied up with our essence as things that exist. To elaborate, we might say that understanding and reason are constituted and accessed in every age in which man exists (no matter even whether we view reason and understanding as ahistorical like Kant or not). Third, and most importantly these phenomena together unite the ancient world's conception of itself with the modern world's conception of itself: in essence, they are the two main tendencies of philosophy's comportment towards itself and its world that have been present since philosophy's inception. Let's explain this last point.
For indeed, if the "modern" was present in ancient times, this would seem to be nonsensical. But no: Hegel, mostly through his reading of Aristotle (indeed, it is obvious he held Aristotle to be the greatest and most useful of all philosophers) felt that philosophy from its inception held both a tendency to explain itself and its world in terms of understanding, of nous, as well as a tendency to explain itself in terms of something more wide ranging than nous, whether it be the Idea, being, the good, doxa, the law, or something else. In the modern times this second something has become "reason"--and as reason gets at the heart of all these various other terms (i.e. Idea, being, etc.). Understanding is more subjective, reason more lawlike, more objective. Nous is more like an individual event of apprehension, reason is more like a universal principle, embracing all entities. Now, the combination these two tendencies together happens constantly in philosophy, but usually only by a picking of one over the other: that is, they only combine such that one is particularly suborrdinate to the other. Thus in ancient philosophies, reason was less dominant and the thinking of nous characterized most thought in some way. The reverse is true for modern times. The two philosophers who have accomplished most thoroughly the combination of the two, the suspension of both in a playful and productive tension are Aristotle and Kant: both address the understanding and bring it into relation with reason, and vice versa. However, neither, Hegel thinks, have adequately developed a philosophy that comprehended and explicated the unity of these two poles: it is his task to do so.
With this in mind, he says the following, which we will explicate a different time.

The understanding determines, and holds the determinations fixed; reason is negative and dialectical , because it resolves the determinations of the understanding into nothing; it is positive because it generates the the universal and comprehends the particular therein.
-Science of Logic, Preface to the First Edition, 28.

Notice how both the understanding, as a phenomenon that determines in its apprehension, is brought into a unity with its opposite, reason, which undoes these determinations or fixing-acts. It is in perceiving this unity that Hegel is truly revolutionary, and at the same time adequately addresses modes of thought that are ancient and modern with a respect for their findings and orientations. With Hegel begins a way of philosophizing that unifies all the rest of philosophy, and thus articulates its development not as a series of arguments disproved by the coming on the scene of a newer philosophy, but as a genuine history of the development of basic concepts that only get renamed and refined over the years. In other words, with Hegel, suddenly philosophy is also a historicism.