I was having a conversation about memory and reality with a friend, and my friend posed this question:
If two people have a conversation (in which we are sure they are the only participants), and each of them proceed to forget the conversation, did it really happen?
I understood, and was sympathetic to, the point my friend was driving at about how memory shapes subjective reality, but from a strictly logical perspective, I had to answer with, “of course the conversation happened, because you just said it did.” (That wasn’t my verbatim answer, because I hadn’t yet thought the whole thing through. But it is the answer I reached after thinking about the matter.) It seems like almost too obvious a thing to point out, but clearly my friend hadn’t noticed, and people doing thought experiments probably miss things like this all the time. If you put it into terms of logic, it would look like this, I guess:
Let “two people had a conversation” be represented by c
and “the participants then forgot the conversation” by f
my friend says:
c & f
This is probably all very dry and unexciting sounding. But it led me to realize two things which I think are interesting. The one, more specific realization, is that the question my friend was asking would be better restated as “how would the world in which the pair forgot the conversation differ from the world in which they remembered it?” Which is kind of a mundane question, which you can probably think of many individual examples to demonstrate. The tougher philosophical question might be “What happens to forgotten events? Where do they go?” (tentative answer: fuck if I know.) The second, more general realization is that this problem is unavoidable when engaged in the God-play of hypothetical scenarios, because you can’t invent a set of circumstances and then take them back or undo them. Do that, and you’re just creating a different, unrelated scenario. Sure, you could do it if you were writing a novel and were going for the “unreliable narrator” thing, but it’s a poor way to make any kind of argument. Be on your guard against this, it can be a subtle trap.