Here’s a puzzle. Suppose you are investigating the ethics of cognition-enhancing drugs. You are presently not such a drug-user, and trust your abilities to think about ethical issues. You examine the issues carefully, spending as much time to gather information as one might care to specify, and you come to the conclusion that taking such drugs is permissible.
So you then take the drugs. When you are on the drugs, you think about the same issue, but while on the drugs, you judge that your earlier conclusion was mistaken: you now think that taking the drugs is wrong, and you identify a particular source of the mistake in the reasoning on behalf of the permissibility conclusion.
The drugs wear off. Then in your unenhanced state, you recall what you thought in your enhanced state, but now think what you did originally: taking the drugs is permissible and your drug-induced insights were mistaken. And you think that your enhanced self made a mistake in thinking that a mistake had been identified in one’s original reasoning for the permissibility conclusion.
So you once again take the drugs, and the process keeps getting repeated.
The puzzle is at what point, and why, irrationality of opinion sets in, for either or both selves. It is pretty clear that the original opinion can easily be rational, and that in the first drug-enhanced state, the second conclusion can be rational as well. One would think, however, that enough vascillating between opinions would undermine at least one of the opinions. But which one and why, and how much vascillation is needed to yield the result? Or maybe we just get unstable rationality no matter the track record?
I won’t say what I think yet.