Earlier we discussed why there is something rather than nothing. We then considered why some things are distinct from another, but only with respect to formal distinctions. And even the discussion of formal distinctions did not really get to the root of the question, since it was based on the idea of opposites, and opposites are already distinct from one another.

The real question about distinction is why it exists at all, whether formal or material, and why reality is not simply one in every way, as Parmenides held.

Previously we discussed the order of the concepts distinction, unity, whole and part, many, first and second, origin, and cause. Some things that follow from these discussions:

1. When two things are distinct, each of the two is in some way one.
2. The two things themselves exist in some way as a whole and as one, and each of the two is a part of that whole.
3. The two in some way have an order of first and second.
4. The second is in some way from the first.

But it does not follow that one of the two is the cause of the other. The reason for this is that causality adds explanation, and the order of first and second in step four here may simply be arbitrary. I have two hands, and one of them must be first when I count them. But I could count them in the opposite order and nothing would be lost. Thus the specific order here does not add to understanding my hands, and so one hand is not a cause of the other.

We can consider possible answers to the question about distinction:

First, someone could say that since distinction is a being of reason, it does not exist in reality. Therefore every statement involving distinction is false: it is false that the chair in my room is not the table, and true that the chair is the table. This would basically be the position of Parmenides, and violates common sense in the deepest possible way. The violation of common sense is sufficient reason to reject this explanation.

Second, someone could say that since distinction is a being of reason, it has nothing positive in itself, and therefore it needs no explanation. This position would admit that it is true that one of my hands is not the other hand, but would assert that there simply is no reason why it is not. This would be somewhat akin to Bertrand Russell’s position that there does not need to be any explanation for the world. This position seems rather unlikely. It makes some sense that there could be a necessary being that is intelligible in itself, and this is necessary to respond to the question of why there is something rather than nothing. But this answer to the question about distinction implies that there is non-being which is either intelligible in itself, or intelligible in no way, yet truly is present in the world. This makes much less sense, and would likely result in depriving the world first of intelligibility in general, and consequently of other kinds of meaning such as purpose and the good.

Third, someone could admit that distinction requires an explanation. This implies that distinction has causes. The material cause, of course, is the beings themselves that are distinct, while the formal cause is the not-being-the-other that each of them possess. But in order to get a full explanation, we need an efficient cause and a final cause. And since two distinct beings seem to be distinct by their very nature, the only way to get an efficient cause is for at least one of the two beings to have an efficient cause itself.

These answers seem to be exhaustive. Either distinction is truly present in the world or it is not; and either it needs an explanation or it does not. The third answer seems by far the most reasonable one.

It is easy to see that accepting this third answer implies accepting that there is one first efficient cause which is the cause of everything else in reality, and corresponding to this, one ultimate end of all things. For we have already argued that causality always implies a first. But if first efficient causes are many, then they will be distinct from one another, and by this argument at least one of them will have an efficient cause, which is a contradiction. Therefore first efficient causes are not many; and thus there is only one.

It should be noted that if one makes this argument in the context of Catholic theology, the first cause that the argument arrives at would not be God the Trinity, but the person of the Father. For the argument explains all distinction, and therefore it would also explain the distinction between the persons of the Trinity. This also has some bearing on the different terminology used by the East and the West in relation to the divine persons. St. Thomas discusses this difference:

The Greeks use the words “cause” and “principle” indifferently, when speaking of God; whereas the Latin Doctors do not use the word “cause,” but only “principle.” The reason is because “principle” is a wider term than “cause”; as “cause” is more common than “element.” For the first term of a thing, as also the first part, is called the principle, but not the cause. Now the wider a term is, the more suitable it is to use as regards God, because the more special terms are, the more they determine the mode adapted to the creature. Hence this term “cause” seems to mean diversity of substance, and dependence of one from another; which is not implied in the word “principle.” For in all kinds of causes there is always to be found between the cause and the effect a distance of perfection or of power: whereas we use the term “principle” even in things which have no such difference, but have only a certain order to each other; as when we say that a point is the principle of a line; or also when we say that the first part of a line is the principle of a line.

According to our treatment the Greeks were right in wishing to use the term “cause.” Cause is indeed narrower than principle, but only by implying explanation, and this is found in the Trinity. It does not imply diversity of substance, while the meaning of “dependence” in St. Thomas’s text here is unclear. Nor does causality, according to our discussion, imply a distance of perfection or power. It is true that the first part of a line is not necessarily the cause of the line, but only insofar as the fact that it is first lacks explanatory value. Insofar as it has such value, as by being a material cause, it also has causality.