To what extent does Descartes dream argument threaten our knowledge of the external world?
Answer by Martin Jenkins
In the first Meditation of his Meditations on the First Philosophy, (1641), Descartes is seeking for a secure, indubitable foundation on which to base human knowledge. He begins by exploring what he perceives by means of his senses.
The senses have been and are deceptive so cannot be afforded uncritical accuracy. Yet surely they cannot be excluded from providing perception tout court? Descartes writes that he is aware of him sitting by a fire, attired in a dressing gown with a paper in his hand. To doubt the truth of this would be an act of madness — on a par with people who suffer from delusions and hallucinations.
Yet when sleeping, Descartes remarks that he dreams of equally improbable things — such as being seated by the fire ‘whilst all the time I was lying undressed in bed!’. So, he concludes that there are no certain marks distinguishing waking from sleeping. Surely the images experienced in dreams are copies and compositions of perceptions experienced when awake as they do display a certain regularity. More, such copies and compositions are based on the corporeal nature of objects in the world experienced when awake. Objects of a corporeal nature display extension, shape, quantity and magnitude and endure through time and in space. Disciplines which deal with such objects such as arithmetic, geometry employ content that is ‘certain and indubitable’.
“For whether I am awake or dreaming, 2 and 3 are 5, a square has no more than four sides; and it does not seem possible that truths so evident can ever be suspected of falsity.”
So there are certain truths which, whether sleeping or awake, are beyond doubt. These deal with a real, independently existing world that continues to exist when we are sleeping. Objects are real and sleeping with dreams is precisely that. Unfortunately, such ‘a priori’ truths can be doubted as, contends Descartes towards the end of Meditation One, a malevolent demon can be deceiving him into thinking they are correct.
The ‘Dream Argument’ begins Descartes dialectic of questioning what can be construed as providing Truth and certainty. In itself, I don’t think it threatens our knowledge of an external world. Firstly, the distinction between dreaming and not dreaming is employed which betrays an already existing epistemological understanding between the two. This distinction is pace G.E. Moore, part of our everyday, natural living. Secondly, the distinction between dreaming and waking can be upheld on the grounds that regularity and order are experienced when awake; whereas dreaming is qualitatively different. Thirdly, the questions can only be asked by means of Language. Language is arguably socially acquired and used. This presupposes the existence of other human beings existing in a social world. So the very use of language refutes the sceptical doubts Descartes is pondering.