How might a person know that the world outside of their mind (the ‘external world’) exists? Those who doubt that we can know that it does are called ‘sceptics’. Both René Descartes (1596–1650) and G. E. Moore (1873–1958) disagreed with scepticism, but each had a different idea about how we could know it to be false.
Descartes built his proof of the external world from his indubitable starting point that he exists. For Descartes, while both our experiences of the world and our memories are doubtable (after all, they could have been put into our heads by an evil demon!), the belief that we who experience thoughts exist is not: so long as I am here to doubt my own existence, I must exist, at least as a nonphysical mind (hence ‘cogito ergo sum’ – I think, therefore, I am). From this basis, Descartes determines, based on purely experience-independent reasoning, that there must also be a God who is responsible for his existence, and that God, being all good and all powerful, would not be a deceiver. So, we are ok to trust in our perceptions of the outside world after all. By contrast, Moore, a firm champion of common sense, believed that we ought to have more faith in our perceptual experiences to begin with. With the sceptics, Moore agrees (as most would), that if we don’t know we’re not just brains housed in vats somewhere, then we can’t know that any of our beliefs about the external world are true. However, he draws an opposing conclusion from this. The sceptic thinks that we can’t know for certain that we’re not just brains in vats, so we ought not to trust in any of our beliefs about the external world. However, Moore believes that we do know certain of our beliefs about the external world to be true: we know we have hands, for example, for here they are, and we can wave them about! Therefore, we can know the hypothesis that we might simply brains in vats to be false. Argumentative manoeuvres of this kind are hence known as ‘Moorean shifts’. | |||