The Question of Doubt
The following exploration of the question of Doubt has been written as a limited introduction. For further information consult the resource list at the end.
Terminology
Doubt: to be uncertain about. In philosophy, 'doubt' can refer to the kind of extreme doubt expressed by René Decartes (French mathematician and philosopher, 1596–1650), who invited us to suspend judgment on everything where even the slightest doubt were possible.
Skepticism: the view that we can never know anything for certain because there is always some ground for doubting, even when it comes to our most fundamental beliefs.
Epistemology: the branch of philosophy known as 'the theory of knowledge'. Epistemology deals with all questions regarding our capacity to know.
Common-sense realism: the picture of the external world we receive through our senses and commonly accept as accurate.
The Issue
In Descartes' First Meditation, titled 'What can be called into doubt', Descartes attempts to remove all his notions of knowledge and belief, peeling away everything that cannot be known for certain to see what remains. His goal: to discover what is certain. His conclusion: '(I) am finally compelled to admit that there is not one of my former beliefs about which a doubt may not properly be raised.' Descartes has three central arguments to support this position: 1/ that our senses deceive us; 2/ that we could be dreaming; and 3/ that a malicious demon could be tricking us. But while his conclusion in this Meditation is extreme doubt, Descartes says that it is extremely difficult to hold this concept in mind. Our beliefs, it seems, are as hard to hold back as the tide.
In order to know something we must have sufficient grounds for knowing it. How can we know anything with certainty when the input we rely on to provide these sufficient grounds is itself uncertain?
Some Argy-Bargy
Descarte's first point is undeniable - our senses do indeed deceive us. It is highly unlikely that the world is exactly as it appears to be, and this provides strong support for his position of doubt. See Making Sense of our Senses for a perspective on the limitations of sensory information.
Descartes second point is 'there are never any sure signs by means of which being awake can be distinguished from being asleep' and this calls into doubt all his experiences. While many believe that the 'I could be dreaming' argument is convincing and therefore supportive of doubt, it may not, ultimately, be true. I argue that there are good reasons to believe that we dream in a different geometry to waking experience. If this is correct, it would be a sure differentiator between being awake and being asleep. This 'Argument from Geometry' can be found in The Atheist Afterlife.
Descarte's third point invokes a supernatural 'explanation' to support his position, but in the modern world a supernatural explanation is no explanation at all. The principle of Ockham's Razor, which may be stated as 'the explanation requiring the fewest assumptions is most likely to be correct' enables us to remove the malicious demon from the equation - as it only adds another layer that requires explanation - leaving us with our malicious (well, unreliable at least) senses.
Descartes' First Meditation raises important questions such as: Is there anything we can know for certain?, Can we build a knowledge base without underlying certainty?, Should we be looking for certainty in the first place, or can we proceed from probabilities?, and, would it be better to talk about different degrees of certainty?
And the winner is?
How innovative and brave to apply the tool of extreme doubt to strip oneself of all that is uncertain and see what remains? I'm inclined to think that the winner is Descartes. In his Second Meditation, Descartes finds his sufficient ground for knowledge in his celebrated 'Cognito ergo sum' - I think therefore I am - although these actual words appear in his Principles of Philosophy.
The skeptical position is more robust than common-sense realism due to the latter's reliance on sense perception. Sense perception can only, at best, give a partial picture of reality, and it often gives a picture that is false. If Descartes were commenting on his First Meditation today (he wrote in the mid 1600's), he may concede - owing to the success of the scientific method - that even if there is nothing that we can know for certain - not even 'I think therefore I am' - we can successfully know things on the basis of probabilities, and successfully proceed from these foundations.
Resources
René Descartes' First Meditation, 'What can be called into doubt'.
Philosophy: The Basics - Nigel Warburton, Chapter Four 'The External World'. Warburton also explores four theories of perception that are more sophisticated than common-sense realism. Available in the Bookshop.
The Philosophy Gym - Stephen Law, Chapter Three 'Brain-Snatched'. Available in the Bookshop.
Reading Philosophy - Guttenplan/Hornsby/Janaway.