SECONDARY CAUSALITY.
109. In determining in the last chapter the conditions of true causality, I spoke only ofabsolutecausality; the reason of this, which I shall now explain, turns on the difference between the first cause and second causes.
110. We have seen that the pure idea of absolute causality is the perception of three conditions: the necessity ofone thing for the existence of another; the sufficiency of the first alone for the existence of the second; and lastly (when the cause is free) the act of the will necessary for the production of the effect. These three conditions are fulfilled absolutely in the first cause, since nothing can exist unless God exists; and for the existence of any object the existence of God, with the free will of creating the object, is sufficient. It is evident that causality cannot be applied in the same sense to second causes; of none of them can it be said that its existence is absolutely necessary for the existence of the effect, since God could have produced it either by means of another secondary agent, or immediately by himself; neither is its existence alone sufficient for the existence of the effect, since whatever exists presupposes and requires the existence of the first cause.
111. Thus, then, the idea of causality applied to God has a very different meaning from that which it has when applied to second causes: it is necessary to bear this in mind, and not to raise questions concerning second causes before the meaning of the wordcauseis strictly defined. It is certain that the relation of an effect to its cause is a relation of dependence; but we have seen that the words dependence, connection, condition, etc., are susceptible of different meanings; if they are not clearly and strictly determined it is impossible to give any solution to these questions.
112. What then is meant by secondary causality? After the observations which we have made, it is not difficult to say. In the order of created beings A will be the cause of B when the following conditions are fulfilled.
I. That the existence of A is necessary (according to the order established) for the existence of B; which may be expressed by this formula: if B exists, A exists or has existed.
II. That in the order established B and A form a series which goes back to the first cause, without the concurrence of the terms of any other series being requisite.
This last condition will not, perhaps, be understood, unless explained by some examples.
113. The motion of my pen is the effect of the motion of my hand; here I have the true relation of secondary causality, for I pass through a series of conditions, which do not require the conditions of any other series: the motion of the pen depends on the motion of my hand; that of my hand depends on the animal spirits (or whatever cause physiologists may please to assign); that of the animal spirits depends on the command of my will; and my will depends on God, who created it, and preserves it. I here find a series of second causes to which I give the true character of causality, in so far as it can exist in a secondary order; and the efficient cause, the principal among secondary causes is my will; because in the secondary order of it is the first term of the series. The motion of the pen of my secretary depends on my will, not however as its true efficient cause, but as its occasion; because in the secretary is found the same series as in the former example: the first term of this series is his will, which I cannot absolutely determine, since being free, it determines itself. There is true efficient causality in the will of the secretary; because there ends the series whose first term is at my disposal only in an improper sense, that is to say, so long as the secretary pleases.
114. The body, A, in motion strikes upon the body, B at rest: the motion of the body A is the cause of the motion of the body B, and the causality will be found in all the terms of the series, that is, in all the motions whose successive communication has been necessary in order that the motion might reach the body B. Let us suppose that inthe series of these communications obstacles have been removed which impeded the communication of the motion; the removal of the obstacles is an indispensable condition on the supposition that they existed, but it is not a true cause, since it is a term foreign to the series of the communications, and might not have existed, without the motion therefore ceasing to exist. For, supposing there had been no obstacles, they would not have been removed, and yet the motion would have been communicated. But it is not the same with respect to the terms which form the series of the communications; for if we represent them by A. B. C. D. E. F. . . . . . . . . . the motion of A cannot reach F if one of the intermediate bodies serving as the vehicle of the communication be taken away.
115. From this theory it follows that the idea of secondary causality represents a concatenation of various objects forming a series, which terminates in the first cause, whether by a necessary order, as in the phenomena of corporeal nature, or by the medium of a first term in the secondary order with a determination of its own, as is the case in things which depend on free will.