Aristotle, says in the Metaphysics, that:
All philosophers agree that the Principles of Change are Contraries
And that they act on some Other; he admits it's hard to establish whether they are in toto - two, or three.
I interpret this to mean, thinking Contraries are Unity of Opposites.
that the Contrary being a Pair of Opposites is two, and the Other being a one; and together we have three
or the Contrary being a Unity, is one, and the Other being a one, we have two.
Hegel reduces this to One (one as a quantity, and also as the Parmenidian One); uniting Being and Becoming - they are opposites, notably; and identifying this with Being (not Becoming); obtains an emanationist cosmology:
(SL 21.70) Pure Being and Pure Nothing are therefore the same; the truth is neither Being, nor Nothing; but rather that Being has passed over into Nothing, and Nothing into Being.
And in the same paragraph he adds:
Their truth is therefore this movement of the immediate vanishing of the one into the other: Becoming
Also, a little later, in remark 3:
The unity, whose moments, Being and Nothing, are inseperable, is at the same time different from these moments. It thus stands as a third with respect to them - a third which, in its most proper form, is Becoming.
When Being achieves determination, this is Matter; and the dialectic of Becoming sublated into Matter, acts:
Existence proceeds from Becoming...it is not mere being, but existence, or Dasein, according to its German etymology, it is Being (Sein) in a certain Place (Da)...with the Concrete Whole is in the form of being, of immediacy, constitutes Determinateness.
This is Hegels notion of dialectical materialism.