(6) That the Cause of any event is an Immediate Antecedent follows from its being an unconditional one.  For if there are three events, A B C, causally connected, it is plain that A is not the unconditional antecedent of C, but requires the further condition of first giving rise to B. But that is not all; for the B that gives rise to C is never merely the effect of A; it involves something further.  Take such a simple case as the motion of the earth round the sun (neglecting all other conditions, the other planets, etc.); and let the earth’s motion at three successive moments be A B C:  A is not the whole cause of B in velocity and direction; we must add relation to the sun, say x.  But then, again, the cause of C will not be merely Bx, for the relation to the sun will have altered; so that we must represent it as Bx’.  The series, therefore, is Ax Bx’ C. What is called a “remote cause” is, therefore, doubly conditional; first, because it supposes an intervening cause; and secondly, because it only in part determines the conditions that constitute this intervening cause.

The immediacy of a cause being implied in its unconditionalness, is an important clue to it; but as far as the detection of causes depends upon sense-perception, our powers (however aided by instruments) are unequal to the subtlety of Nature.  Between the event and what seems to us the immediate antecedent many things (molecular or etherial changes) may happen in Chemistry or Physics.  The progress of science would be impossible were not observation supplemented by hypothesis and calculation.  And where phenomena are treated upon a large scale, as in the biological and social sciences, immediacy, as a mark of causation, must be liberally interpreted.  So far, then, as to the qualitative character of Causation.

(7) But to complete our account of it, we must briefly consider its quantitative character.  As to the Matter contained, and as to the Energy embodied, Cause and Effect are conceived to be equal.  As to matter, indeed, they may be more properly called identical; since the effect is nothing but the cause redistributed.  When oxygen combines with hydrogen to form water, or with mercury to form red precipitate, the weight of the compound is exactly equal to the weight of the elements combined in it; when a shell explodes and knocks down a wall, the materials of the shell and wall are scattered about.  As to energy, we see that in the heavenly bodies, which meet with no sensible impediment, it remains the same from age to age:  with things ‘below the moon’ we have to allow for the more or less rapid conversion of the visible motion of a mass into other forms of energy, such as sound and heat.  But the right understanding of this point involves physical considerations of some difficulty, as to which the reader must refer to appropriate books, such as Balfour Stewart’s on The Conservation of Energy.