One way of looking at the difference would be to say that while the left hemisphere's raison d'être is to narrow things down to a certainty, the right hemisphere's is to open them up into possibility. In life we need both. In fact for practical purposes, narrowing things down to a certainty, so that we can grasp them, is more helpful. But it is

As Pascal wrote, ‘The ultimate achievement of reason is to recognize that there are an infinity of things which surpass it. It is indeed feeble if it can't get as far as understanding that.’

The left hemisphere is not in touch with the world. It is demonstrably self-deceiving, and confabulates – makes up a story, when it cannot understand something, and tells it with conviction. Michael Gazzaniga first demonstrated this in split-brain patients. Subsequent research shows that, unlike the right hemisphere, which tends toward self-doubt,

Only the left hemisphere encodes tools and machines – you will remember that the purpose of the left hemisphere is to allow us to manipulate the world, not to understand it.

The right hemisphere seems to be involved more with new experience, new events, things, ideas, words, skills or music, or whatever it may be, while they are still fresh, original and unique, and so to speak present, to the mind. The right hemisphere's world is present – or more precisely ‘presences’ to us, as Heidegger puts it. By contrast the left

More than that, physics teaches us that, at the most fundamental level of existence, there simply are no discrete pieces of inert matter. Instead there are clusters of interrelated probabilistic events that change their nature when observed. In the words of the great physicist Richard Feynman, quantum mechanics deals with ‘nature as she is –

The right hemisphere, the so-called minor hemisphere, is in fact the one that knows, and more importantly the one that understands, more.

Some elegant research into gesture and speech reveals that thought begins and ends in the right hemisphere, passing through the necessary staging post of the left hemisphere, where it is put into serial sentences. This follows a typical pattern in the way the hemispheres relate: the origins and the end lie in the right hemisphere's world, but it is

I am just as sceptical of the naïve idealist view, espoused by some post-modernists, that reality is all in our heads – we make it all up. For one thing there would be no point in my writing this, since you don't exist to read it. I take it that we bring about a world in consciousness that is partly what is given, and partly what we bring,