HO HOW WE WE DO DO KNOW

Of course, reality could all be an illusion, but proving it one way or the other is surprisingly difficult, says Mike Holderness

PHILOSOPHERS are not being rude  when they describe the approach most of us take as naive realism. After all, when they cross the street on the way to work, they tend to accept implicitly – as we all do –  that there is an external reality that exists independently of our observations of it.  But at work, they have to ask: if there is, how can we know? In other words, the question “what exists?” reduces, for what in philosophy passes for practical purposes, to questions such as “what do we mean by ‘know’?” Plato had a go at it 2400 years ago, defining “knowledge” as “justified true belief”. But testing the justification or the truth of beliefs traces back to our perceptions, and we know these can deceive us. Two millennia later, René Descartes decided to work out what he was sure he knew. Legend has it that he climbed into a large stove to do so in warmth and solitude. He emerged declaring that the only thing he knew was that there was something that was doubting everything. The logical conclusion of Descartes’s doubt is solipsism, the conviction that one’s own consciousness is all there is. It’s an idea that is difficult to refute. Samuel Johnson’s notoriously bluff riposte to the questioning of the reality of objects – “I refute it thus!”, kicking a stone holds no philosophical water. As Descartes pointed out a century earlier, it is impossible to know we are not dreaming. Nor has anyone had much luck making sense of dualism – the idea that mind and matter are distinct. One response is that there is only matter, making the mind an illusion that arises from neurons doing their thing. The opposite position is “panpsychism”, which attributes mental properties to all matter. As the astrophysicist Arthur Eddington expressed it in 1928: “the stuff of the world is  mind-stuff...  not altogether foreign to the feelings in our consciousness”. Quite separately, rigorous logicians such as Harvard’s Willard Van Orman Quine abandoned the search for a foundation of reality and took “coherentist” positions. Let go of the notion of a pyramid of knowledge, they argued: think instead of a raft built out of our beliefs, a seaweedy web of statements about perceptions and statements about statements, not “grounded” in anything but hanging together and solid enough to set sail upon. Or even, possibly, to be a universe. This idea is circular, and it’s cheating, say critics of a more foundationist bent. It leads back to the suspicion that there actually is no reality independent of our observations. But if there is – how can we know?  ■