# Necessity, Possibility, and Impossibility

I spoke here about various kinds of necessity, but did not explain the nature of necessity in general. And in the recent post on Hume’s idea of causality, it was not necessary to explain the nature of necessity, because the actual idea of causality does not include necessity. Thus for example a ball can break a window even if it would have been possible for someone to catch the ball, but the person did not do so.

Sometimes it is asked whether necessity implies possibility: if it is necessary that Tuesday follow Monday, it is possible for Tuesday to follow Monday? I am inclined (and I think most are inclined) to say yes, on the grounds that to say that something is not possible is normally understood to imply that the thing is impossible; thus if it is not possible for Tuesday to follow Monday, it is impossible. But this is largely a verbal question: regardless of how we answer this, the real point is that the necessary is the same kind of thing as the possible, except that possibilities are many while the necessary is one. And likewise, a count of zero for the same things implies impossibility. Thus there is something that we are counting: if we find none of them, we speak of an impossibility. If we find only one, we speak of one necessity. And if we find many, we speak of many possibilities.

What are we counting here? Let’s take an example. Horses can be white, or red, or brown, among other possibilities. So there are many possible colors for a horse. And on the other hand snow is always white (or so let us pretend.) So there is only one possible color for snow, and so snow is “necessarily” white. Meanwhile, air is always colorless (or so let us pretend.) So it is impossible for air to have a color. Based on this example, we propose that what we are counting is the number of forms that are suitable for a given matter. Someone might object that if we analyze the word “suitable” here it might involve some sort of circularity. This may well be the case; this is a common occurrence, as with desire and the good, and with virtue and happiness. Nonetheless, I think we will find it worthwhile to work with this definition, just as in those earlier cases.

# Revisiting Russell on Cause

We discussed Bertrand Russell’s criticism of the first cause argument here. As I said there, he actually suggests, although without specifically making the claim, that there is no such thing as a cause, when he says:

That argument, I suppose, does not carry very much weight nowadays, because, in the first place, cause is not quite what it used to be. The philosophers and the men of science have got going on cause, and it has not anything like the vitality it used to have.

This is absurd, and it is especially objectionable that he employs this method of insinuation instead of attempting to make an argument. Nonetheless, let me attempt to argue on Russell’s behalf for a moment. It is perhaps not necessary for him to say that there is no such thing as a cause. Suppose he accepts my account of cause as an explanatory origin. Note that this is not purely an objective relationship existing in the world. It includes a specific relationship with our mind: we call something a cause when it is not only an origin, but it also explains something to us. The relatively “objective” relationship is simply that of origin.

A series of causes, since it is also a series of explanations, absolutely must have a first, since otherwise all explanatory force will be removed. But suppose Russell responds: it does not matter. Sure, this is how explanations work. But there is nothing to prevent the world from working differently. It may be that origins, namely the relationship on the objective side, do consist of infinite series. This might make it impossible to explain the world, but that would just be too bad, wouldn’t it? We already know that people have all sorts of desires for knowledge that cannot be satisfied. A complete account of the world is impossible in principle, and even in practice we can only obtain relatively local knowledge, leaving us ignorant of remote things. So you might feel a need of a first cause to make the world intelligible, Russell might say, but that is no proof at all that there is any series of origins with a first. For example, consider material causes. Large bodies are made of atoms, and atoms of smaller particles, namely electrons, protons, and neutrons. These smaller particles are made of yet smaller particles called quarks. There is no proof that this process does not go on forever. Indeed, the series would cease to explain anything if it did, but so what? Reality does not have to explain itself to you.

In response, consider the two following theories of water:

First theory: water is made of hydrogen and oxygen.

Second theory: every body of water has two parts, which we can call the first part and the second part. Each of the parts themselves has two parts, which we can call the first part of the first part, the second part of the first part, the first part of the second part, and the second part of the second part. This goes on ad infinitum.

Are these theories true? I presume the reader accepts the first theory. What about the second? We are probably inclined to say something like, “What does this mean, exactly?” But the very fact that the second theory is extremely vague means that we can probably come up with some interpretation that will make it true, depending in its details on the details of reality. Nonetheless, it is a clearly useless theory. And it is useless precisely because it cannot explain anything. There is no “causality” in the second theory, not even material causality. There is an infinite series of origins, but no explanation, and so no causes.

The first theory, on the other hand, is thought to be explanatory, and to provide material causes, because we implicitly suppose that we cannot go on forever in a similar way. It may be that hydrogen and oxygen are made up of other things: but we assume that this will not go on forever, at least with similar sorts of division.

But what if it does? It is true, in fact, that if it turns out that one can continue to break down particles into additional particles in a relatively similar manner ad infinitum, then “water is made of hydrogen and oxygen” will lose all explanatory force, and will not truly be a causal account, even in terms of material causes, even if the statement itself remains true. It would not follow, however, that causal accounts are impossible. It would simply follow that we chose the wrong account, just as one would be choosing wrongly if one attempted to explain water with the second theory above. The truth of the second theory is irrelevant; it is wrong as an explanation even if it is true.

As I have argued in a number of places, nature is not in the business of counting things. But it necessarily follows from this that it also does not call things finite or infinite; we are the ones who do that. So if you break down the world in such a way that origins are infinite, you will not be able to understand the world. That is not the world’s problem, but your problem. You can fix that by breaking down the world in such a way that origins are finite.

Perhaps Russell will continue to object. How do you know that there is any possible breakdown of the world which makes origins finite? But this objection implies the fully skeptical claim that nothing can be understood, or at least that it may turn out that nothing can be understood. As I have said elsewhere, this particular kind of skeptical claim implies a contradiction, since it implies that the same thing is known and unknown. This is the case even if you say “it might be that way,” since you must understand what you are saying when you say it might be that way.

# Reductionist vs Anti-Reductionist Dichotomy

I started this post with a promise to return to issues raised by this earlier one. I haven’t really done so, or at least not as I intended, basically because it simply turned out that there was still too much to discuss, some but not all of which I discussed in the last two posts. I am still not ready to return to those original issues. However, the purpose of this post is to keep the promise to explain the relevance of my rejection of both reductionism and anti-reductionism to my account of form. To some extent this has already been done, but a clearer account is possible.

Before going through this kind of consideration, I expect almost everyone to accept implicitly or explicitly an account which maintains one or the other side of this false dichotomy. And consequently, I expect almost everyone to find my account of form objectionable.

Reductionists in general will simply deny the existence of form: there is nothing that makes a thing one, because nothing is actually one. We might respond that if you are reducing things to something else, say to quarks, there still must be something that makes a quark one. The reductionist is likely to respond that a quark is one of itself, and does not need anything else to make it one. And indeed, you might satisfy the general definition of form in such a way, but at that point you are probably discussing words rather than the world: the question of form comes up in the first place because we wonder about the unity of things composed of parts. Thus, at any rate, the most a reductionist will concede is, “Sure, in theory you can use that definition.” But they will add, “But it is a badly formed concept that will mostly lead people away from the truth.” The error here is analogous to that of Parmenides.

Anti-reductionists will admit the existence of form, but they will reject this account, or any other account which one actually explains in detail, because their position implicitly or explicitly requires the existence of hidden essences. The basic idea is that form should make a thing so absolutely one that you cannot break it down into several things even when you are explaining it. It is very obvious that this makes explanation impossible, since any account contains many words referring to many aspects of a thing. I mentioned Bertrand Russell’s remark that science does not explain the “intrinsic character” of matter. Note that this is precisely because every account, insofar as it is an account, is formal, and form is a network of relationships. It simply is not an “intrinsic character” at all, insofar as this is something distinct from such a network. Anti-reductionism posits form as such an intrinsic character, and as such, it requires the existence of a hidden essence that cannot be known in principle. The error here is basically that of Kant.

There is something in common to the two errors, which one might put like this: Nature is in the business of counting things. There must be one final, true answer to the question, “How many things are here?” which is not only true, but excludes all other answers as false. This cannot be the case, however, for the reasons explained in the post just linked. To number things at all, whether as many or as one, is to apply a particular mode of understanding, not to present their mode of being as such.

I expect both reductionists and anti-reductionists to criticize my account at first as one which belongs to the opposite side of this dichotomy. And if they are made aware that it does not, I expect them to criticize it as anti-realist. It is not, or at any rate not in a standard sense: I reject this kind of anti-realism. If it is anti-realist, it is anti-realist in a much more reasonable way, namely about “not being something,” or about distinction. If one thing is not another, that “not another” may be a true attribution, but it is not something “out there” in the world. While the position of Parmenides overall is mistaken, he was not mistaken about the particular point that non-being is not being.

# Really and Truly True

There are two persons in a room with a table between them. One says, “There is a table on the right.” The other says, “There is a table on the left.”

Which person is right? The obvious answer is that both are right. But suppose they attempt to make this into a metaphysical disagreement.

“Yes, in a relative sense, the table is on the right of one of us and on the left of the other. But really and truly, at a fundamental level, the table is on the right, and not on the left.”

“I agree that there must be a fundamental truth to where the table is. But I think it is really and truly on the left, and not on the right.”

Now both are wrong, because it is impossible for the relationships of “on the right” and “on the left” to exist without correlatives, and the assertion that the table is “really and truly” on the right or on the left means nothing here except that these things do not depend on a relationship to an observer.

Thus both people are right, if they intend their assertions in a common sense way, and both are wrong, if they intend their assertions in the supposed metaphysical way. Could it happen that one is right and the other wrong? Yes, if one intends to speak in the common sense way, and the other in the metaphysical way, but not if they are speaking in the same way.

In the Mathematical Principles of Natural Philosophy, Newton explains his ideas of space and time:

I. Absolute, true, and mathematical time, of itself, and from its own nature flows equably without regard to anything external, and by another name is called duration: relative, apparent, and common time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion, which is commonly used instead of true time; such as an hour, a day, a month, a year.

II. Absolute space, in its own nature, without regard to anything external, remains always similar and immovable. Relative space is some movable dimension or measure of the absolute spaces; which our senses determine by its position to bodies; and which is vulgarly taken for immovable space; such is the dimension of a subterraneous, an æreal, or celestial space, determined by its position in respect of the earth. Absolute and relative space, are the same in figure and magnitude; but they do not remain always numerically the same. For if the earth, for instance, moves, a space of our air, which relatively and in respect of the earth remains always the same, will at one time be one part of the absolute space into which the air passes; at another time it will be another part of the same, and so, absolutely understood, it will be perpetually mutable.

III. Place is a part of space which a body takes up, and is according to the space, either absolute or relative. I say, a part of space; not the situation, nor the external surface of the body. For the places of equal solids are always equal; but their superfices, by reason of their dissimilar figures, are often unequal. Positions properly have no quantity, nor are they so much the places themselves, as the properties of places. The motion of the whole is the same thing with the sum of the motions of the parts; that is, the translation of the whole, out of its place, is the same thing with the sum of the translations of the parts out of their places; and therefore the place of the whole is the same thing with the sum of the places of the parts, and for that reason, it is internal, and in the whole body.

IV. Absolute motion is the translation of a body from one absolute place into another; and relative motion, the translation from one relative place into another. Thus in a ship under sail, the relative place of a body is that part of the ship which the body possesses; or that part of its cavity which the body fills, and which therefore moves together with the ship: and relative rest is the continuance of the body in the same part of the ship, or of its cavity. But real, absolute rest, is the continuance of the body in the same part of that immovable space, in which the ship itself, its cavity, and all that it contains, is moved. Wherefore, if the earth is really at rest, the body, which relatively rests in the ship, will really and absolutely move with the same velocity which the ship has on the earth. But if the earth also moves, the true and absolute motion of the body will arise, partly from the true motion of the earth, in immovable space; partly from the relative motion of the ship on the earth; and if the body moves also relatively in the ship; its true motion will arise, partly from the true motion of the earth, in immovable space, and partly from the relative motions as well of the ship on the earth, as of the body in the ship; and from these relative motions will arise the relative motion of the body on the earth. As if that part of the earth, where the ship is, was truly moved toward the east, with a velocity of 10010 parts; while the ship itself, with a fresh gale, and full sails, is carried towards the west, with a velocity expressed by 10 of those parts; but a sailor walks in the ship towards the east, with 1 part of the said velocity; then the sailor will be moved truly in immovable space towards the east, with a velocity of 10001 parts, and relatively on the earth towards the west, with a velocity of 9 of those parts.

While the details of Einstein’s theory of relativity may have been contingent, it is not difficult to see that Newton’s theory here is mistaken, and that anyone could have known it at the time. It is mistaken in precisely the way the people described above are mistaken in saying that the table is “really and truly” on the left or on the right.

For example, suppose the world had a beginning in time. Does it make sense to ask whether it could have started at a later time, or at an earlier one? It does not, because “later” and “earlier” are just as relative as “on the left” and “on the right,” and there is nothing besides the world in relation to which the world could have these relations. Could all bodies have been shifted a bit in one direction or another? No. This has no meaning, just as it has no meaning to be on the right without being on the right of something or other.

In an amusing exchange some years ago between Vladimir Nesov and Eliezer Yudkowsky, Nesov says:

Existence is relative: there is a fact of the matter (or rather: procedure to find out) about which things exist where relative to me, for example in the same room, or in the same world, but this concept breaks down when you ask about “absolute” existence. Absolute existence is inconsistent, as everything goes. Relative existence of yourself is a trivial question with a trivial answer.

Yudkowsky responds:

Absolute existence is inconsistent

Wha?

Yudkowsky is taken aback by the seemingly nonchalant affirmation of an apparently abstruse metaphysical claim, which if not nonsensical would appear to be the absurd claim that existence is impossible.

But Nesov is quite right: to exist is to exist in relation to other things. Thus to exist “absolutely” would be like “being absolutely on the right,” which is impossible.

Suppose we confront our original disputants with the fact that right and left are relative terms, and there is no “really true truth” about the relative position of the table. It is both on the right and on the left, relative to the disputants, and apart from these relationships, it is neither.

“Ok,” one responds, “but there is still a deep truth about where the table is: it is here in this room.”

“Actually,” the other answers, “The real truth is that it is in the house.”

Once again, both are right, if these are taken as common sense claims, and both are wrong, if this is intended to be a metaphysical dispute where one would be true, the real truth about where the table is, and the other would be false.

Newton’s idea of absolute space is an extension of this argument: “Ok, then, but there is still a really true truth about where the table is: it is here in absolute space.” But obviously this is just as wrong as all the other attempts to find out where the table “really” is. The basic problem is that “where is this” demands a relative response. It is a question about relationships in the first place. We can see this in fact even in Newton’s account: it is here in absolute space, that is, it is close to certain areas of absolute space and distant from certain other areas of absolute space.

Something similar will be true about existence to the degree that existence is also implicitly relative. “Where is this thing in the nature of things?” also requires a relative response: what relationship does this have to the rest of the order of reality? And in a similar way, questions about what is “really and truly true,” if taken to imply an abstraction from this relative order, will not have any answer. In a previous post, I said something like this in relation to the question, “how many things are here?” Reductionists and anti-reductionists disputing about whether a large object is “really and truly a cloud of particles” or “really and truly a single object,” are in exactly the same position as the disputants about the position of the table: both claims are true, in a common sense way, and both claims are false, if taken in a mutually exclusive metaphysical sense, since speaking of one or many is already to involve the perspective of the knower, in particular as knowing division and its negation.

Of course, an anti-reductionist has some advantage here because they can respond, “Actually, no one in a normal context would ever call a large object a cloud of particles. So it is not common sense at all.” This is true as far as it goes, but it is not really to the point, since no one denies in a common sense context that large objects also consist of many things, as a person has a head, legs, and arms, and a chair has legs and a back. It is not that the “cloud of particles” account is so much incorrect as it is adopting a very unusual perspective. Thus someone on the moon might say that the table is 240,000 miles away, which is a very unusual thing to say of a table, compared to saying that it is on the left or on the right.

None of this is unique to the question of “how many.” Since there is an irreducible element of relativity in being itself, we will be able to find some application to every question about the being of things.

# Being and Unity II

Content warning: very obscure.

This post follows up on an earlier post on this topic, as well on what was recently said about real distinction. In the latter post, we applied the distinction between the way a thing is and the way it is known in order to better understand distinction itself. We can obtain a better understanding of unity in a similar way.

As was said in the earlier post on unity, to say that something is “one” does not add anything real to the being of the thing, but it adds the denial of the division between distinct things. The single apple is not “an apple and an orange,” which are divided insofar as they are distinct from one another.

But being distinct from divided things is itself a certain way of being distinct, and consequently all that was said about distinction in general will apply to this way of being distinct as well. In particular, since being distinct means not being something, which is a way that things are understood rather than a way that they are (considered precisely as a way of being), the same thing applies to unity. To say that something is one does not add something to the way that it is, but it adds something to the way that it is understood. This way of being understood is founded, we argued, on existing relationships.

We should avoid two errors here, both of which would be expressions of the Kantian error:

First, the argument here does not mean that a thing is not truly one thing, just as the earlier discussion does not imply that it is false that a chair is not a desk. On the contrary, a chair is in fact not a desk, and a chair is in fact one chair. But when we say or think, “a chair is not a desk,” or “a chair is one chair,” we are saying these things in some way of saying, and thinking them in some way of thinking, and these ways of saying and thinking are not ways of being as such. This in no way implies that the statements themselves are false, just as “the apple seems to be red,” does not imply that the apple is not red. Arguing that the fact of a specific way of understanding implies that the thing is falsely understood would be the position described by Ayn Rand as asserting, “man is blind, because he has eyes—deaf, because he has ears—deluded, because he has a mind—and the things he perceives do not exist, because he perceives them.”

Second, the argument does not imply that the way things really are is unknown and inaccessible to us. One might suppose that this follows, since distinction cannot exist apart from someone’s way of understanding, and at the same time no one can understand without making distinctions. Consequently, someone might argue, there must be some “way things really are in themselves,” which does not include distinction or unity, but which cannot be understood. But this is just a different way of falling into the first error above. There is indeed a way things are, and it is generally not inaccessible to us. In fact, as I pointed out earlier, it would be a contradiction to assert the existence of anything entirely unknowable to us.

Our discussion, being in human language and human thought, naturally uses the proper modes of language and thought. And just as in Mary’s room, where her former knowledge of color is a way of knowing and not a way of sensing, so our discussion advances by ways of discussion, not by ways of being as such. This does not prevent the way things are from being an object of discussion, just as color can be an object of knowledge.

Having avoided these errors, someone might say that nothing of consequence follows from this account. But this would be a mistake. It follows from the present account that when we ask questions like, “How many things are here?”, we are not asking a question purely about how things are, but to some extent about how we should understand them. And even when there is a single way that things are, there is usually not only one way to understand them correctly, but many ways.

Consider some particular question of this kind: “How many things are in this room?” People might answer this question in various ways. John Nerst, in a previous discussion on this blog, seemed to suggest that the answer should be found by counting fundamental particles. Alexander Pruss would give a more complicated answer, since he suggests that large objects like humans and animals should be counted as wholes (while also wishing to deny the existence of parts, which would actually eliminate the notion of a whole), while in other cases he might agree to counting particles. Thus a human being and an armchair might be counted, more or less, as 1 + 10^28 things, namely counting the human being as one thing and the chair as a number of particles.

But if we understand that the question is not, and cannot be, purely about how things are, but is also a question about how things should be understood, then both of the above responses seem unreasonable: they are both relatively bad ways of understanding the things in the room, even if they both have some truth as well. And on the other hand, it is easy to see that “it depends on how you count,” is part of the answer. There is not one true answer to the question, but many true answers that touch on different aspects of the reality in the room.

From the discussion with John Nerst, consider this comment:

My central contention is that the rules that define the universe runs by themselves, and must therefore be self-contained, i.e not need any interpretation or operationalization from outside the system. As I think I said in one of the parts of “Erisology of Self and Will” that the universe must be an automaton, or controlled by an automaton, etc. Formal rules at the bottom.

This is isn’t convincing to you I guess but I suppose I rule out fundamental vagueness because vagueness implies complexity and fundamental complexity is a contradiction in terms. If you keep zooming in on a fuzzy picture you must, at some point, come down to sharply delineated pixels.

Among other things, the argument of the present post shows why this cannot be right. “Sharply delineated pixels” includes the distinction of one pixel from another, and therefore includes something which is a way of understanding as such, not a way of being as such. In other words, while intending to find what is really there, apart from any interpretation, Nerst is directly including a human interpretation in his account. And in fact it is perfectly obvious that anything else is impossible, since any account of reality given by us will be a human account and will thus include a human way of understanding. Things are a certain way: but that way cannot be said or thought except by using ways of speaking or thinking.

# The Error of Parmenides

Come now, I will tell thee—and do thou hearken to my saying and carry it away— the only two ways of search that can be thought of. The first, namely, that It is, and that it is impossible for it not to be, is the way of belief, for truth is its companion. The other, namely, that It is not, and that it must needs not be,— that, I tell thee, is a path that none can learn of at all. For thou canst not know what is not—that is impossible— nor utter it; . . . . . . for it is the same thing that can be thought and that can be.

As I pointed out here, the error here comes from an excessive identification of the way a thing is known and the way a thing is. But he does this only in a certain respect. We evidently think that some things are not other things, and that there are many things. So it would be easy enough to argue, “It is the same thing that can be thought and that can be. But we can think that one thing is not another, and that there are many things. So one thing can fail to be another, and there can be many things.” And this argument would be valid, and pretty reasonable for that matter. But Parmenides does not draw this conclusion and does not accept this argument. So his claim that what can be thought and what can be are the same must be taken in a more particular sense.

His position seems to be that “to be” has one and only one real meaning, in such a way that there is only one way for a thing to be. Either it is, or it isn’t. If it is, it is in the only way a thing can be; and if it is not, it is not in the only way a thing can be. But this means that if it is not, it is not at all, in any way, since there is only one way. And in this case it is not “something” which is not, but nothing. Thus, given this premise, that there is only one way to be, Parmenides’s position would be logical.

In reality, in contrast, there is more than one way to be. Since there is more than one way to be, there can be many things, where one thing is in one way, and another  thing is in another way.

Even granting that there is more than one way to be, Parmenides would object at this point. Suppose there is a first being, existing in a first way, and a second being, existing in a second way. Then the first being does not exist in the second way, and the second being does not exist in the first way. So if we say that “two beings exist,” how do they exist? The two do not exist in the first way, but only the first one does. Nor do the two exist in the second way, but only the second one does. And thus, even if Parmenides grants for the sake of argument that there is more than one way to be, he can still argue that this leads to something impossible.

But this happens only because Parmenides has not sufficiently granted the premise that there is more than one way to be. As I pointed out in the discussion of being and unity, when two things exist, the two are a pair, which is being in some way, and therefore also one in some way; thus the two are “a pair” and not “two pairs.” So the first being is in one way, and the second being is in a second way, but the two exist in still a third way.

The existence of whole and part results from this, along with still more ways of being. “The two” are in a certain respect the first, and in a certain respect the second, since otherwise they would not be the two.

Thus we could summarize the error of Parmenides as the position that being is, and can be thought and said, in only one way, while the truth is that being is, and can be thought and said, in many ways.

# The Actual Infinite

There are good reasons to think that actual infinities are possible in the real world. In the first place, while the size and shape of the universe are not settled issues, the generally accepted theory fits better with the idea that the universe is physically infinite than with the idea that it is finite.

Likewise, the universe is certainly larger than the size of the observable universe, namely about 93 billion light years in diameter. Supposing you have a probability distribution which assigns a finite probability to the claim that the universe is physically infinite, there is no consistent probability distribution which will not cause the probability of an infinite universe to go to 100% at the limit, as you exclude smaller finite sizes. But if someone had assigned a reasonable probability distribution before modern physical science existed, it would very likely have been one that make the probability of an infinite universe go very high by the time the universe was confirmed to be its present size. Therefore we too should think that the universe is very probably infinite. In principle, this argument is capable of refuting even purported demonstrations of the impossibility of an actual infinite, since there is at least some small chance that these purported demonstrations are all wrong.

Likewise, almost everyone accepts the possibility of an infinite future. Even the heat death of the universe would not prevent the passage of infinite time, and a religious view of the future also generally implies the passage of infinite future time. Even if heaven is supposed to be outside time in principle, in practice there would still be an infinite number of future human acts. If eternalism or something similar is true, then an infinite future in itself implies an actual infinite. And even if such a theory is not true, it is likely that a potentially infinite future implies the possibility of an actual infinite, because any problematic or paradoxical results from an actual infinite can likely be imitated in some way in the case of an infinite future.

On the other hand, there are good reasons to think that actual infinities are not possible in the real world. Positing infinities results in paradoxical or contradictory results in very many cases, and the simplest and therefore most likely way to explain this is to admit that infinities are simply impossible in general, even in the cases where we have not yet verified this fact.

An actual infinite also seems to imply an infinite regress in causality, and such a regress is impossible. We can see this by considering the material cause. Suppose the universe is physically infinite, and contains an infinite number of stars and planets. Then the universe is composed of the solar system together with the rest of the universe. But the rest of the universe will be composed of another stellar system together with the remainder, and so on. So there will be an infinite regress of material causality, which is just as impossible with material causality as with any other kind of causality.

Something similar is implied by St. Thomas’s argument against an infinite multitude:

This, however, is impossible; since every kind of multitude must belong to a species of multitude. Now the species of multitude are to be reckoned by the species of numbers. But no species of number is infinite; for every number is multitude measured by one. Hence it is impossible for there to be an actually infinite multitude, either absolute or accidental.

We can look at this in terms of our explanation of defining numbers. This explanation works only for finite numbers, and an infinite number could not be defined in such a way, precisely because it would result in an infinite regress. This leads us back to the first argument above against infinities: an infinity is intrinsically undefined and unintelligible, and for that reason leads to paradoxes. Someone might say that something unintelligible cannot be understood but is not impossible; but this is no different from Bertrand Russell saying that there is no reason for things not to come into being from nothing, without a cause. Such a position is unreasonable and untrue.