The second paragraph of Descartes’ Meditations says this:
But, to this end, it will not be necessary for me to show that the whole of these are false–a point, perhaps, which I shall never reach; but as even now my reason convinces me that I ought not the less carefully to withhold belief from what is not entirely certain and indubitable, than from what is manifestly false, it will be sufficient to justify the rejection of the whole if I shall find in each some ground for doubt. Nor for this purpose will it be necessary even to deal with each belief individually, which would be truly an endless labor; but, as the removal from below of the foundation necessarily involves the downfall of the whole edifice, I will at once approach the criticism of the principles on which all my former beliefs rested.
I love Descartes, but I don’t agree with him here. He says above, “my reason convinces me that I ought not the less carefully to withhold belief from what is not entirely certain and indubitable, than from what is manifestly false”. In other words, if I can’t be absolutely certain, then I shouldn’t believe it.
It seems to me that that standard is irrationally high.Descartes says reason convinces him of it, but reason convinces me of the opposite.
Descartes’ standard of belief is “if there is any possible way in which I could be wrong, then I shouldn’t believe it”. I don’t see how we, as finite humans, can possibly have the kind of certainty Descartes seeks.
In the second meditation, Descartes argues that we can be absolutely certain we exist because we experience ourselves thinking, and thinking implies existence.
1. If something does not exist, it cannot think.
2. I think.
3. Therefore, I exist.
That seems like a good argument, but it makes some assumptions.It assumes that we know what “something” and “existence” and “thinking” and “I” mean, for instance: that these are well-defined terms that can be used unambiguously in the argument above. The argument assumes that we have a world in which there are certain things which exist separate from other things, that existence itself is a clear category rather than being a spectrum from things that mostly exist to things that barely exist, that thinking is clearly what we are doing when we wonder if we exist, and so on. Let me be clear. I think these are good assumptions. I believe them. But I don’t think that they are absolutely certain, that it is impossible for them to be false. So they don’t have the kind of certainty Descartes requires.
Furthermore, for the argument to work, we have to be sure that it is logically valid. The argument pattern above is well-known. It’s even got a name: modus tollens. I agree with philosophers in identifying it as a trustworthy logical form. I cannot even imagine how it might be false. But it doesn’t follow that we can be absolutely certain of it.
It seems very clear that we cannot be absolutely certain of anything. That’s not a problem, though. Certainty is overrated.
Some philosophers after Descartes argued that the only reason we can think at all, the only reason we can even form logical categories to think with, is that we have available to us a whole bunch of assumptions about how thinking works and what concepts mean and how they are interrelated.There is just no way for us to clear all of them away and start reasoning with no prior knowledge at all. We can’t even think coherently without them.
This doesn’t commit me to skepticism. I am not saying we don’t know anything. Knowledge has to do with justified belief. We can know lots of things, but only because we do not need absolute certainty about them in order to know them.
Because we can be certain of nothing, and because we need to assume something to think at all, it is rational to accept some things as true even though we can see a way in which they could theoretically be false. There are truths which are not certain and indubitable, but to which I should assent. Reason convinces me of this.