Sec. 5.  The understanding of the complex nature of Causes and Effects helps us to overcome some other difficulties that perplex the use of these words.  We have seen that the true cause is an immediate antecedent; but if the cause is confounded with one of its constituent conditions, it may seem to have long preceded the event which is regarded as its effect.  Thus, if one man’s death is ascribed to another’s desire of revenge, this desire may have been entertained for years before the assassination occurred:  similarly, if a shipwreck is ascribed to a sunken reef, the rock was waiting for ages before the ship sailed that way.  But, of course, neither the desire of revenge nor the sunken rock was ‘the sum of the conditions’ on which the one or the other event depended:  as soon as this is complete the effect appears.

We have also seen the true effect of any state and process of things is the immediate consequence; but if the effect be confounded with one of its constituent factors, it may seem to long outlive the cessation of the cause.  Thus, in nearly every process of human industry and art, one factor of the effect—­a road, a house, a tool, a picture—­may, and generally does, remain long after the work has ceased:  but such a result is not the whole effect of the operations that produce it.  The other factors may be, and some always are, evanescent.  In most of such works some heat is produced by hammering or friction, and the labourers are fatigued; but these consequences soon pass off.  Hence the effect as a whole only momentarily survives the cause.  Consider a pendulum which, having been once set agoing, swings to and fro in an arc, under the joint control of the shaft, gravitation and its own inertia:  at every moment its speed and direction change; and each change may be considered as an effect, of which the antecedent change was one condition.  In such a case as this, which, though a very simple, is a perfectly fair example of all causation, the duration of either cause or effect is quite insensible:  so that, as Dr. Venn says, an Effect, rigorously conceived, is only “the initial tendency” of its Cause.

Sec. 6.  Mill contrasted two forms under which causation appears to us:  that is to say, the conditions constituting a cause may be modified, or ‘intermixed’ in the effect, in two ways, which are typified respectively by Mechanical and Chemical action.  In mechanical causation, which is found in Astronomy and all branches of Physics, the effects are all reducible to modes of energy, and are therefore commensurable with their causes.  They are either directly commensurable, as in the cases treated of in the consideration of the mechanical powers; or, if different forms of energy enter into cause and effect, such as mechanical energy, electrical energy, heat, these different forms are severally reducible to units, between which equivalents have been established.  Hence Mill calls this the “homogeneous intermixture of effects,” because the antecedents and consequents are fundamentally of the same kind.