Posterior Analytics (Bouchier)/Book II/Chapter XII

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Chapter XII: On the Causes of events which exist, are in process, have happened, or will happen[edit]

The Cause is the same for past, existing, proceeding and future occurrences, and is always the middle term. It may be simultaneous with or anterior to its effect. In circular demonstrations causes may be inferred from their effects and vice versâ. Probable effects have probable causes.

The same cause as that which produces existing things applies also to things which are in process, have happened and will happen, for in all these cases the middle term is the cause. Existing things, however, require an existing cause, things in process a like cause, things past a past cause, things future a future cause. For instance, to the question ‘Why did an eclipse take place?’ the answer is ‘because the earth was interposing.’ It will take place because the earth will interpose: it does take place because the earth does interpose. Again: What is ice? It may be assumed that it is frozen water. Let C represent Water; A Frozen; B the middle term or cause, namely a total failure of heat. Now B is true of C, and A, frozen, of B. Hence, Ice is being produced when B is in process, has been produced when B has taken place, and will be produced when it does take place. Thus this kind of cause and its effect occur together when they occur at all, they are in process together, do exist, will exist and have existed simultaneously.

In cases, however, where cause and effect are not simultaneous, it may be asked whether, as would appear to be the case, some things are the causes of others which immediately follow them. E.g. Can one thing in process be the cause of another’s being in process; is it a future cause which produces a future effect, or a past cause a past effect? Now one may deduce a cause from the effects which have followed it, and in this case the starting point lies in the past. On the other hand one cannot draw an inference from the cause concerning the effect, e. g. that because such a thing has happened some particular effect must have followed. So too with future events. Whether the time intervening between cause and effect be indefinite or definite one cannot say that ‘because this has happened, such and such an effect must also have occurred.’ In the interval between the cause and the effect it would be incorrect to say that the latter had occurred, though the cause had already appeared. The same argument applies to future events. When one thing has happened another thing is not necessarily about to happen. The cause or middle term ought to belong to the same genus as the effect, being, in the case of past events, past, of future events, future, of events in process, in process also, of existing events, existing; but past and future cannot be homogeneous in this way. Further, the interval between cause and effect cannot be indefinite nor, until the effect is produced, can it be definite, for during the whole of that interval it would be false to say that the effect exists.

Here we ought to examine the meaning of ‘Uniformity of Nature,’ owing to which a thing when it has once happened is inclined to happen again. But is it not clear that what is in process is not a continuation of that which is past, that one past event is not a continuation of another, and that everything which is past is an ultimate and indivisible, past events being in fact no more contiguous to one another than are points, both of which are indivisible? The same reasoning shews that the present is not merely a continuation of the past, for an event in process is divisible, a past event indivisible. An event in process really bears the same relation to a past event as a line bears to a point.

Infinite past events go to make up that which is now in process. These subjects must, however, be discussed more clearly in the general treatment of Motion (Cf. Phys. Bk. vi). With regard to the manner in which the middle can be the cause when the result is continuous, this much may suffice. In these cases also the primary term and the middle must both be ultimates. For instance, suppose A to have taken place because C has taken place,[1] C however coming later than A. Now the starting point is C, because it is nearer to the present moment, which forms the starting point in time. Now C has taken place if D has taken place; and when D has taken place A must previously have taken place. The cause of this is C, for when D has taken place it is necessary that C should have taken place, and when C has taken place, it is necessary that A should have done so before. If the middle term be thus expressed it might be asked whether the process must sometime reach an ultimate and terminate, or whether a middle term would always appear and so produce an infinite regress, for as was said a past event is not a continuation of another past event. Yet one must begin with the middle term and with the present moment as a primary point of departure. The same is true of future events: for if it be true to say that the effect D will be, it must be a previous truth that the cause A will be. The cause of this is C, for if D will be, C will be previously, but if C will be A will be previously. Thus in these cases also an infinite subdivision is possible, for future events likewise are not bound together in perfect continuity, and in the case of them also an ultimate starting point must be assumed.

The same thing applies to matters of production. E.g. If a house has been built the stones must have been cut and have existed. What is the reason of this? Because, for a house to be built, a foundation must have been laid. If so, stones must have existed previously. Similarly, if there is to be a house, walls also must exist beforehand. This too is proved by means of the same middle term, namely, that a foundation must be laid before the house can be built.

We see with regards to matters in process that production is effected in a circular manner, and we observe that this may happen when the major and minor and also the middle terms are each of them consequences of the other, and it is then that Conversion takes place. Now we proved at the outset (Pr. An. II. 5–7) that causes and effects may be proved circularly, and that is the meaning of the circular process. In the case of matters of production the method may be regarded as follows. When the earth has been moistened vapours must arise. When that happens a cloud is produced. From the cloud comes rain, and as a result of the rain the earth must be moistened. Hence the process has returned to its starting point, and when any one of the terms is present another follows, when that is present a third follows, and when the third is present the first recurs again.

Some events in process are universal, for they exist or come into existence always and in every instance; others are not invariable but Probable. E.g. Not every man can grow a beard, but this is usually so. In such cases the middle term also must be of ordinary application. If A be predicated of B universally, and B of C universally also, then A must be predicated as invariable attribute of C, always present in every instance of it (for so we may paraphrase the expressions ‘universal,’ ‘distributive,’ and ‘eternal’). Our hypothesis was, however, that the attribute was only ordinarily present in the subject, and therefore the middle term B must be probable also. It follows then that things which exist or come into existence ordinarily but not invariably must also possess certain ultimate starting points or first principles.


  1. E. g. the foundations of a house may be known to have been laid when the house is seen, though the latter came into existence after the former.