Consider this contrast: religious studies teaches you what people believe. Philosophy , on the other hand, teaches you how to think. Religious studies tells you how the universe was viewed by people who lived a couple of millennia ago, and what they thought this implied for how we should behave. Philosophy examines logic and reasoning, how we get and validate knowledge, the methods of investigating nature, and the justifications that have been offered for various moral attitudes and practices. It asks searching questions about rights, wrongs and the responsibilities we have to each other, it discusses arguments about how society should be organised, and it challenges the assumptions that underlie systems of thought and, indeed, our own personal thinking - the assumptions we learned from parents, school and society.

Above all, philosophy teaches you to examine, criticise, question, investigate, explore, discuss, listen, respond to the force of argument and evidence, persist with difficult and complicated notions, and accept that some questions have no answers but nevertheless that it is eminently worth wondering what answers might be possible - for as Paul Valéry said: “A difficulty is a light; but an insurmountable difficulty is the sun!”

Religious studies tells you what people long ago thought those answers were.

The power of reason

Which class would you want your child to attend - religious studies or philosophy?

It is one of the biggest clichés in contemporary education, but no less true for being one, that the biggest gift we educators can give to our pupils is the power of critical thinking.

We do not know what the world will be asking, in 20 or 30 years’ time, of the people now in school and university. The rate of change in all spheres of social and economic life is very fast, and getting faster. There is only one way to train people for the unknown: to make them nimble-minded, flexible, good at learning, good at problem-solving, good at seeing things from different points of view, good evaluators of what people claim, and adept at finding information and applying it aptly.

The biggest gift we can give our pupils is the power of critical thinking

Add to these skills an understanding of how arguments are constructed, how knowledge is acquired and assessed in different fields of enquiry, and how one searches out the hidden premises and assumptions which almost all kinds of thinking involve, and you have a smart person.

TS Eliot said: “There is only one method: to be intelligent.” Philosophy is about fostering intelligence. Really fostering intelligence.

It is also, en route to this highly desirable result, a fascinating survey of the story of human thought, for philosophy began as the study of everything, and over its long rich life it found answers and methods which allowed parts of itself to become independent, turning into powerful world-changing enquiries: the natural sciences, psychology, sociology, linguistics, logic, artificial intelligence and cognitive science were all born from philosophy.

Plato lived nearly a thousand years before Christianity became the official religion of the Roman Empire; almost every word we use in science, psychology, politics, ethics and education is a word of ancient Greek origin, because the concept denoted by the word is one that the Greek philosophers brought into the light of reason.

An oddity of our educational system is that from the rich history of human thought just one thread is filleted out - religion - and given an inflated importance, therefore.

The world views and ethics of the historical religions are thin gruel in comparison with the amazing wealth of philosophical reflection in history; we are depriving our children of real intellectual adventure by restricting them to so feeble a thing.

In a full-blown history of ideas, it would be seen how the human mind has grown and matured well past the religions’ starting points; the power of intellect growing with the growth of knowledge as philosophy and its offspring, the natural and social sciences, have brought more and more of the universe within the range of exploration.

Philosophy requires, and therefore encourages, both imagination and analysis. It requires both the fine details and the large horizons of thought to be seen with equal clarity. It teaches the lesson that Walter Pater said we must learn: that it is only the dullness of the eye that makes any two things seem alike. It teaches fearlessness in the face of ideas and, therefore, open-mindedness. It is an education in itself.

‘Proper’ philosophy

With Dr John Taylor, of Cranleigh School, as the lead organiser, a group of us is working on a GCSE in philosophy - proper philosophy, not a quasi-subterfuge version as with the A-level philosophy and ethics, which is really ‘philosophy of religion and ethics”. Among other things, it recognises that there is both lively interest and real aptitude among pupils in Years 9 to 11 for philosophical thought.

The new religious studies GCSE has squeezed philosophy out, inexplicably - and at its own risk, because when it goes head-to-head with a proper philosophy GCSE, the betting will be on the latter. So a proper philosophy GCSE is needed.

Philosophy requires, and encourages, imagination and analysis

In fact, philosophical talent exists in all youngsters; children as young as 5 are very good at showing it, as wonderfully highlighted by the work of the Philosophy Foundation.

Encouraging philosophical thinking is a powerful support to the rest of the curriculum, as shown when “ToK” (aka “Theory of Knowledge”) in the International Baccalaureate is well taught. Philosophy in school - proper philosophy in school - would do that for everyone.

Professor AC Grayling is a philosopher and master of New College of the Humanities