…though the cause has an effect and is at the same time itself effect, and the effect not only has a cause but is also itself cause, yet the effect which the cause has, and the effect which the cause is, are different, as are also the cause which the effect has, and the cause which the effect is.
But now the outcome of the movement of the determinate causal relation is this, that the cause is not merely extinguished in the effect and with it the effect, too, as in formal causality, but that the cause in being extinguished becomes again in the effect, that the effect vanishes in the cause, but equally becomes again in it. Each of these determinations sublates itself in its positing, and posits itself in its sublating; what is present here is not an external transition of causality from one substrate to another; on the contrary, this becoming-other of causality is at the same time its own positing. Causality therefore presupposes its own self or conditions itself.
G.W.F.Hegel, Hegel’s Science of Logic, Trans., A.V.Miller, Humanities Press, New York, 1976, 565-566