In my under graduate studies Dr. Alspector-Kelly remarked, while studying the problem of induction, there is also a problem of deduction. This problem of induction is infamous, but the problem of deduction has gained little attention in comparison. The problem of induction is the problem of validating the mode of inference.Thus the problem of deduction is the same. How can we validate that deduction actually works? Couldn’t an descartian devil fool us into believing deduction works when it doesn’t? If a devil could do such a thing, how can we trust deduction? These question appear very disturbing. Deduction is often considered the bedrock of good reasoning. The bring it into question is to question all we hold dear, epistemically speaking.
One of my thoughtful friends responded that we know deduction is valid because that inference works in every possible world. The problem with this line of thinking is that we have no reason to trust deductive reasoning in fact works in every possible world. If we are willing to grant that problem of deduction could be a problem, then that inference appearing to work in every possible world is also suspect.
The real issue with this problem is that once it is granted as a problem, there is no solution. Take this inference:
2. If A then B
If this can truly be questioned there is no saving argument.Thankfully, there is no way to undermine deduction. We can be asked to think about a devil fooling us. But when we ask for specifics, we see this question holds no force. How is a devil suppose to trick into deduction working when it doesn’t. It is clear that deduction work. Perhaps this can only be seen for those who have “the light of reason”. But it does not matter that only can see this as long those who do see it are not fooled. If an advocate of the problem of deduction can be more specific on how we can be fooled, perhaps there would be a problem. However, since no specificity exists (to my knowledge) there is no problem of deduction