‘At first, then, quantity as such appears in opposition to quality; but quantity is itself a quality, a purely self-related determinateness distinct from the determinateness of its other, from quality as such. But quantity is not only a quality; it is the truth of quality itself, the latter having exhibited its own transition into quantity. Quantity, on the other hand…is…quality itself in such a manner that apart from this determination there would no longer be any quality as such. The positing of the totality requires the double transition, not only of the one determinateness into its other, but equally the transition of this other, its return, into the first. …quality is contained in quantity, but this is still a one-sided determinateness. That the converse is equally true, namely, that quantity is contained in quality and is equally only a sublated determinateness, this results from the second transition – the return into the first determinateness. This observation on the necessity of the double transition is of great importance throughout the whole compass of scientific method.’
G.W.F.Hegel, Hegel’s Science of Logic, (Vol. I The Objective Logic) Trans., A.V.Miller, Humanities Press, New York, 1976, 323