I am grateful to Stephen Priest, lecturer at Edinburgh University in the 1990s. His book, Theories of the Mind, was the first book of academic philosophy I read cover to cover. His writing was concise and clear. “Idealists believe that the physical is mental. Materialists believe that the mental is physical” is an example of his elegant and easy way of making a profound statement. It was his lectures on Sartre that started me on the long journey away from metaphysical beliefs toward the behaviourist, materialist outlook I now have.

Priest said that his subject dealt with a rag-bag of problems. Once certain speculative questions became answered or even just potentially answerable then they moved on from Philosophy to their own discipline. What was called Natural Philosophy for example became Science once real answers started to emerge. Thus Philosophy is left with all the intractable stuff much of which might never be properly resolved.

Of all these un-answerables I’d say the central one is this: that outside of perception it is impossible to know what exists if anything. There might be nothing at all. Conversely there might be so much that exists outside of perception that our reality is infinitely small by comparison. It could be that what we are able to apprehend and conceive of is a tiny element of a bigger reality. On the other hand what we are able to apprehend might represent all reality to the extent that reality is all perception. There might be nothing objective whatsoever. Ours could be a kind of virtual world created by minds or perhaps even a single absolute mind of which individual minds are a manifestation.

These are the speculations that philosophers have wrestled with for centuries. What is important to know is that a conclusive answer to such speculations is impossible as only by getting outside of the picture to have a look could such an answer be forthcoming. This is the scepticism of knowledge that thinkers come up against and can't get beyond. The problems are intractable. At best metaphors are possible which suggest in symbolic ways what existence there might be beyond the human experience. They give a sense of another reality. All the stories that have been central to religion and philosophy down the centuries are only ever interpretations, pictures, imaginings of how things might be. In the absence of any superior wisdom to officiate we are stuck with these hypothetical models. Of all the philosophical problems that exist this one is at the root.

I don't think being unable to know the absolutes is reason for despair though. The real limitations of knowledge should be defined. Although the great thinkers of history probably set out to find truth and were always left scratching their head with a sense of failure, in so doing they were able to test the limitations of possible knowledge and get a sense of where the boundaries are. The work of Hume and Wittgenstein is instructive here. What lies beyond these boundaries, they say, is best left alone. Actually there is no choice because being transcendent such questions are by definition out of reach.

Says Hume: “When we go through libraries, convinced of these principles [absolutes], what havoc must we make? If we take in our hand any volume - of divinity or school metaphysics, for instance - let us ask, does it contain any abstract reasoning about quantity or number? No. Does it contain any experiential reasoning about matters of fact and existence? No. Then throw it in the fire, for it can contain nothing but sophistry and illusion.” In similar spirit, Wittgenstein advises that what cannot be spoken of must pass over in silence. Although remarks like these may seem defeatist, effectively limiting knowledge to facts and numbers, they can actually be liberating if they provide accuracy about what can and can't be known.

I think a good philosophy is an essential part of mental health. And part of mental health is understanding limitations. Most of the ultimate issues in the human experience are probably beyond reach of the understanding. There is still no shortage of matters to be grappled with that do fall within conceptual powers and it is to these that we should limit our attentions. To do otherwise is to live in illusion as Hume says and that is not good for a healthy mind.

When abstraction, metaphor and myth are used inappropriately then the transcendent appears immanent. God becomes man. This is deceptive leading to misunderstandings about reality. Belief becomes as important as knowledge. This is how religion works, merging fact with fable. A mature humanity concerned with real knowledge would find this unsatisfactory.