‘We hope to explain the entire universe in a single, simple formula you can wear on your T-shirt.’ This statement was made in 1983 by a scientist at Fermi Lab. He went on, ‘I think we’re on the threshold of finding God.’ Presumably he is still working on it. The medieval schoolmen also went in for simple formulae you can wear on your T-shirt: for example, ‘Aliquid est, ergo Deus est’ (Something exists, therefore God exists). This particular formula is based on very little in the way of empirical observation. You can leave your cyclotron at home and still discover that something exists. But where does the ‘therefore’ come from? Does the mere existence of something prove the reality of God?

The First Vatican Council in 1870 stated that the existence of God can be known by human reason without the aid of divine revelation. But today the very principles of human reason are in dispute. The medieval mind ran along a relatively straight track, but the modern mind is faced with a multitude of choices. Realism, Anti-realism, Positivism, Pragmatism, Phenomenology, Deconstruction: each philosophical tradition leads in a different direction, and the man or woman in the street could be forgiven for becoming cynical about the whole business. When I was a philosophy publisher, I saw virtually every philosophical position both attacked and defended by people more educated than myself. And yet, what I became cynical about was not philosophy as such, but rather our system of higher education.

Universities, with few exceptions, do not teach philosophers to understand their predecessors. A professional philosopher needs only to be familiar enough with the work of recent contemporaries to be able to play by the rules of the game. Originality is valued way above the ability to appreciate the truth in another’s point of view. And so we have the spectacle of small groups of philosophers inventing their own language, a jargon only they can understand, partly to exclude outsiders. Phenomenologists do not speak to analysts, logicians ignore critical theorists. Philosophers have more invested in finding sources of disagreement than in finding common ground.

The medieval philosophers, whatever their individual faults and failings, at least still belonged to a tradition that valued truth. They had (for the most part) faith in reason. To rejoin the great conversation of philosophy, and to put the squabbles of the last few generations behind us, we must try to believe that the world makes maximum sense. Even if I do not know what the truth is, I must believe that there is a truth somewhere. For what can I lose by doing this? If I am wrong, and the world is absurd, it would still be a much nobler thing to behave as though it made sense, and by so doing introduce some sense into one corner of it.

But is it really possible that the whole world is senseless? The ‘world’ means simply that which reveals itself to our consciousness. Mind and world cannot be separated. They form a unity. For each one of us, the world is that of which we are aware. It is not something that is hidden from us by the veils of perception, but is precisely what we can see and grasp. And what we grasp points directly to God.

For the world we see is not the kind of thing that has to exist. It is ‘contingent’. The mere fact that it changes proves that it does not have to be what it happens to be at any given moment. Reflection on this fact leads to the idea of a being that would have to exist, a necessary being, one that would be incapable of change. This idea of a ‘necessary being’ is produced simply by negating the quality of contingency we observe in the world.

Of course, possession of the idea of a ‘necessary being’ does not mean we understand what it might be in itself. What we can say is that such a being - whatever it is - would be the only thing that could provide a final level of explanation for the world we experience. It would hold the answer to the final question: ‘Why, if the world need not exist, does it?’ If the world is caused by anything, it is caused by something that cannot not exist. (For if it could not exist, then we would be able to ask of that too, ‘Why does it?’)

There are, however, certain things we can say about a ‘necessary being’. It would have to be a being whose nature, whose very ‘essence’, is to be (esse, in Latin). Therefore it would not be restricted to being any thing in particular, like a tree, or a dog, or a galaxy. All those entities are restricted in one respect or another: necessary being alone would not be restricted by anything. It would contain that which ‘is’ in everything, but without that which ‘is not’. It would be total being, infinite being, simple being. It would include the being of everything that is, but also infinitely more.

To use a mathematical analogy, the number 1 includes every possible fraction, and it is reflected in each (1/2, 1/3, 1/4, etc.). It cannot lack anything that is possessed by the lower realities that come from it, just as for St Thomas esse ‘is not limited in any determined mode of perfection of being but contains in itself the whole of being.’

To many modern philosophers, of course, a being that just existed, and whose essence was existing, would not be infinite but would be a nothing, a non-existent, because ‘it makes sense only to speak of something with some describable properties as existing’ (Anthony O’Hear). St Thomas, surprisingly, would probably have agreed. We cannot use the word ‘exists’ in the same sense to apply both to things and to a necessary being, to restricted being and to Unrestricted Being. The word ‘exists’ means ‘to stand out’; but esse does not stand out. If anything, it stands ‘under’ (subsists). It cannot be known by us in the way that we know the world.

We know things in the world by what they exclude, by their ‘definitions’ (their boundaries). To imagine a thing deprived of boundaries is to see it effectively dissolve into nothingness. What would ‘catness’ become if it did not exclude ‘dogness’, or ‘redness’ if it did not exclude ‘blueness’? To the human imagination, the abstraction of ‘being’ can only mean the reduction of all things to a lowest common denominator, to that infinitely vague quality which they have in common when everything important about them has been extracted or eliminated.

But what if that positive quality that excludes dogness actually came from somewhere or something else? What if the catness (that is what it is because it excludes dogness) was simply an expression of that other thing, just as dogness was an expression of some other quality in that thing, a quality that requires a contrast with catness? After all, what we can imagine or picture to ourselves is not really the point here: what is more important is what we can hypothesize, what we can posit as an explanation for what we find in the world.

Therefore ‘argument from contingency’ does not prove that a being called God exists. It would be more accurate to say it draws our attention to the fact the world is not a sufficient explanation for itself. It gestures towards the (unimaginable) Infinity that would alone explain it, if anything does. Whether that Infinity, that ‘explanation’, is real or not is something we each have to decide. If we affirm it, we are making an act of faith in the ultimate intelligibility of the universe.

So what about the other famous so-called proof of God, the one St Anselm formulated in the Proslogion around 1078, known as the "ontological proof"? Anselm defines God as ‘that than which a greater cannot be thought’. But, he argued, if I am thinking of ‘that than which a greater cannot be thought’, I cannot at the same time think that it does not exist in reality, because for something to exist in reality is greater than for it to exist only in my mind.

Of course, Anselm agrees that it is possible to think that God does not exist. What he argues is that we cannot do so at the same time as thinking of God: for ‘no one who understands the reality that God is, can think that God does not exist.’ To ‘understand the reality that God is’ is not, of course, to grasp the essence of God (which Anselm did not believe was possible), but simply to grasp the concept that identifies what he is – namely, ‘that than which a greater cannot be thought’. To grasp this concept is like looking in a new direction: upwards instead of sideways.

Anselm’s puzzle is misunderstood when it is treated like an attempt to prove the existence of God logically. His definition is simply a trick to make us think of God, the Transcendent, who surpasses every idea we can form of his nature. Think of him as good, or wise, or powerful, and a greater can be thought who is better, wiser or stronger. Think of him as an idea in the mind, and a greater can be thought who is the Maker of the mind and all it contains. Those who reply that, nevertheless, God may not exist whatever I think, have missed the point. They are abstracting themselves from the existential situation Anselm describes. They have placed themselves at one remove from the problem: they are thinking about thinking of God, rather than thinking of God.

Anselm’s trick resembles nothing so much as a Zen koan. The koan is used in Buddhism to trigger a state of nondualistic awareness. The content of this awareness is variously referred to as ‘Mind’, ‘the Essence of Mind’, ‘the Unconscious’, ‘the Buddha’ or ‘Suchness’. Of Mind, Huang-Po says, ‘It has been in existence since the beginningless past, it knows neither birth nor death; …it is beyond the category of being and nonbeing ... for it transcends all limits, words, traces and opposites. It must be taken as it is in itself; when an attempt is made on our part to grasp it in our thoughts, it eludes.’

D.T. Suzuki quotes the following 8th-century conversation in one of his Essays in Zen Buddhism. ‘When it is said to be existent this is not in the sense which people of the world give to it. When it is said to be nonexistent, it is not in the sense which people of the world give to it.’ ‘What kind of thing do you call it, then?’ ‘The term "thing" is inapplicable here.’ ‘If so, what term is applicable?’ ‘No designation is possible. Hence the Unconscious. It is beyond characterization…. To see into where there is no "something" - this is true seeing, this is eternal seeing.’ ‘What is the difference between one who thinks and Suchness itself?’ ‘There is no distinction between the two.’

For the East, the Absolute is as evident as it was for St Thomas and St Anselm, who called it God. Zen may call it the Mind, and imply that it is the Self of the thinker, but the whole point about this ‘Suchness’ is that it transcends the split between subject and object, seer and seen. It is not graspable; it can be ‘known’ only in darkness, in the dazzling darkness that Anselm (following St Paul) calls ‘Inaccessible Light’, adding, ‘whatever I see, I see through it, much as an eye that is weak sees through the light of the sun whatever it sees, although it is unable to see that light in the sun itself’ (XVI).

The first of all numbers cannot be grasped by any of the fractions, just as we cannot grasp God by means of the confused concept of Infinity we get by mentally suppressing the limitations on finite perfections and qualities. Infinity is only ‘grasped’ by not-grasping, by a kind of letting-go, by a mental process at ninety degrees to normal human thinking. That which transcends and unifies the inner and the outer worlds cannot be known in the way we know the outer. It would be more accurate to say that it cannot be known at all: we are the fractions that are known, by the One in whom we live, and move, and have our being. As the Katha Upanishad tells us, ‘Words and thoughts cannot reach him, and he cannot be seen by the eye. How then can he be perceived except by one who says, "He is"?’

And with all this we are still only at the threshold of Christianity – a threshold that, as we have seen, borders the other religions. We cannot know God, though we know that the Absolute exists (in the sense already explored above). We cannot know him; but what if he should share with us his knowledge of himself? What if we were to be invited into the inner life of the One? This is the astounding claim that is made by the Christian faith, which opens a completely new chapter in the history of religion.