Universitas, Number 9, September 2001

The Five Ways and Modern Science

John Ziegler


Maritain's book Approches de Dieu said that the Aquinas 5 ways were still valid (when he wrote). Nowadays, 50 years after that book, there have been many advances in science and philosophy. There are now studies in cosmology and quantum cosmology. I wish to know if the ways are good arguments today.


Maritain was right 50 years ago (the 5 ways of Aquinas are valid) and is right still and will be right regardless of whatever discoveries are made in science (and even in philosophy).

How can I say that?

In the first place, and fundamentally, we must consider science. Now, taken in its widest sense, science is knowledge through causes. In that widest sense, to know anything through its cause is to have science of it. Well, what we usually call science, physics and chemistry and geology and so on, are sciences according to that having of knowledge through causes.

But what sort of cause? You will see that since science is knowledge through causes, then the sort of knowledge of cause determines the sort of science.

Now, there are two ways in which we know cause. One way is that we simply know that something is obviously the cause of something else when we see that there is some reason why the first gives rise to the second. Thus, there is a universal reason why things fall to the ground, called gravity. We know that it is the cause of the falling, but we do not know why it causes the falling.

Or again, we know that the bacilli of tuberculosis give rise to the disease, and we even know how the mechanism of infection works (in part at least), but we do not know more than that.

Now, this sort of knowledge of causes is called knowledge THAT.

The second way is to know why something must necessarily be the cause of something else. Thus, in mathematics, we know that if something is a Euclidean triangle, then its angles necessarily must add up to 180 degrees. There is no possible escape from that, and it must necessarily always be true, despite any future discoveries in the sciences, and even in mathematics.

Or again, in mathematics, we know that adding two and three is a cause of five, and that can never change. That is, in knowing that something is necessarily the cause of something else, we are knowing that it cannot possibly be otherwise.

This sort of knowledge of causes is called knowledge WHEREFORE or WHY. Clearly, mathematics is a science, since it knows through causes, and not only that, it is science WHY.

And so, on the one hand there are the so-called natural sciences. I will call them the experimental sciences: physics, chemistry, geology. All of these know through causes, but it is only known that they are causes, not that they necessarily must be causes so that it cannot be otherwise. Or, to put this another way, they know causes only when some condition is true: thus, given Newton's law of gravitation, then it can be predicted with certainty that planetary orbits will be elliptical.

That is, the experimental sciences know truth, but only conditionally (IF). And this is because they are sciences THAT.

But on the other hand there is, for example, mathematics. We know unconditionally that a Euclidean triangle can always be inscribed in a circle so that all three vertices touch it. This is not conditional knowledge, but absolute and unshakeable and eternal knowledge, and this is because it is science WHY.

Take particular note that science WHY far more fulfils the idea of science than science THAT.

Mathematics, for example, is far more of a science than is physics. And indeed, that is the very reason that physicists and chemists and geologists use mathematics as much as they can in their science: to give it more certitude, although this always remains conditional certitude. So, only science WHY can give knowledge of cause necessarily and forever true.

Now, the five ways of Aquinas come from science WHY.

Let me explain this further.

Mathematics is not actually about reality. That does not mean that it cannot be used to build magnificent bridges or intricate computers, which are very real. No, mathematics deals fundamentally with what can be imagined, but which does not exist 'in the real'. Nobody can make a thing which is a triangle as Euclid imagined it: a plane figure (but any real surface is full of bumps and hollows) with three straight sides (having no thickness, but no real line can be made with no thickness at all: and 'straight' is impossible at least on a microscopic scale; and so on). It can be used to design bridges because the parts of the bridge can be conditionally considered as triangles, arcs, and so on; and the parts of the computer can be designed to do what they do if they behave conditionally according to certain mathematical equations. But they are really only conditionally arcs and triangles.

Likewise, mathematics investigates the nature of numbers. But pure numbers do not exist outside mathematics; but two stones, five persons.

But what about the idea of a science WHY which is about real things? The name of this science is philosophy.

Now, in the second place, with all this said, let us begin to look at what Aquinas said. Let us take the central argument of one of his Ways, actually the second. Nothing exists without a reason. (The whole effort of every science is to discover the reasons things exist.) Well, then, if something does exist (our senses tell us of the world, and we know we exist ourselves) then there must be some reason for its existence. Furthermore, we know that there are various reasons for the existence of things, and these reasons are always something other than the thing in question: a cause. That is, their reason for existence is not their own self.

This needs to be explained. I have said that the things we know are 'reasoned' into existence not by themselves, because to do that they would have to exist: they would have to exist before they existed. To put this in other words, the things we know depend on something else for their existence. If we take things that depend on something for their existence, then what about the 'something', the cause?

If it, too, depends on something else for its existence, we have a question. The question is: could there be something that is its own reason of existence?

Such a being would be without a cause, although not without a reason of existence.

There must be such a thing. Suppose we said that every cause depends on another cause for its existence. Then we would have to say that A is caused by B, which is caused by C.... and so on for ever. In this, there would never be anything in existence to cause in the first place. So, none of the members of the series, C or B or A, could exist because there would be no cause of their existence.

Therefore, it is false to say that every cause depends on another cause for its existence. There must be one cause, the first of the series, which exists by reason of itself, not by reason of another. It must be un-caused.

So, a first cause, itself without a cause, must exist. If things exist at all, there must be an un-caused first cause. And indeed things do exist.

But the un-caused, or first cause, must be such a thing as can cause all the beings, and all their properties, and all their qualities. That is, it must have actually in itself (in some way) all the perfection of all the beings of the world, and of all possible beings. Otherwise there would be something which exists without a reason. But such a being can be nothing else than the being we call God. Therefore God exists, must necessarily exist, and exist regardless of any insights of experimental science, mathematical science, or even philosophical science. It will never be possible to discover something that makes this proof 'invalid', just as it will never be possible to discover something that makes the angles of a Euclidean triangle anything other than 180 degrees, or the square root of forty-nine anything other than seven.

No discoveries in cosmology, astrophysics, quantum electrodynamics, the discovery of quarks, any discovery in genetics, or any other discipline of experimental science can possibly affect those mathematical truths. Nor can they affect the truth that God exists. It is necessarily true (but they are only conditionally true).

John Ziegler

John Ziegler is a lecturer at the Centre for Thomistic Studies, in Sydney, Australia.

This article posted September 2001. It was published in Universitas, No. 9 (2001).
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