exemplify the universal flow of life?  Hegel finds that indeed to be the case.  Concepts we daily use, such as quality and quantity, essence and phenomenon, appearance and reality, matter and force, cause and effect, are not fixed and isolated entities, but form a continuous system of interdependent elements.  Stated dogmatically the meaning is this:  As concavity and convexity are inseparably connected, though one is the very opposite of the other—­as one cannot, so to speak, live without the other, both being always found in union—­so can no concept be discovered that is not thus wedded to its contradiction.  Every concept develops, upon analysis, a stubbornly negative mate.  No concept is statable or definable without its opposite; one involves the other.  One cannot speak of motion without implying rest; one cannot mention the finite without at the same time referring to the infinite; one cannot define cause without explicitly defining effect.  Not only is this true, but concepts, when applied, reveal perpetual oscillation.  Take the terms “north” and “south.”  The mention of the north pole, for example, implies at once the south pole also; it can be distinguished only by contrast with the other, which it thus includes.  But it is a north pole only by excluding the south pole from itself—­by being itself and not merely what the other is not.  The situation is paradoxical enough:  Each aspect—­the negative or the positive—­of anything appears to exclude the other, while each requires its own other for its very definition and expression.  It needs the other, and yet is independent of it.  How Hegel proves this of all concepts, cannot here be shown.  The result is that no concept can be taken by itself as a “that-and-no-other.”  It is perpetually accompanied by its “other” as man is by his shadow.  The attempt to isolate any logical category and regard it as fixed and stable thus proves futile.  Each category—­to show this is the task of Hegel’s Logic—­is itself an organism, the result of a process which takes place within its inner constitution.  And all logical categories, inevitably used in describing and explaining our world, form one system of interdependent and organically related parts.  Hegel begins with an analysis of a concept that most abstractly describes reality, follows it through its countless conflicts and contradictions, and finally reaches the highest category which, including all the foregoing categories in organic unity, is alone adequate to characterize the universe as an organism.  What these categories are and what Hegel’s procedure is in showing their necessary sequential development, can here not even be hinted at.