The only explanation that I can think of that wouldn't be a causal explanation is if the choice to return the wallet just happened. There was no reason, no cause.
Just so. If I choose to return a wallet, that is just a brute fact about the universe. You should feel free to ask the question "Why?" about a pure choice, but I cannot think of any good answers to it. The only way you can get any analytical traction over choices is if you have more than one choice, or if the choices are mixed in with some randomness or some causality.
There was no reason, no cause. It just happened. It could have not happened but in did. That's what we mean by undetermined or random.
Your description is necessary for X to be random, but not sufficient for X to be random. Your description, to me, is just another way of saying that X is not caused. If you think that all things are either caused or random, then you will naturally conclude that a non-caused thing is random. If, however, you start off thinking that all things are caused, random, or chosen, then you will naturally conclude that a non-caused thing is either random or chosen -- it will not occur to you to assume that all non-caused things must be random.
Conversely, what I mean by random is slightly more specific than what you mean by random. When you say "random," you just mean that something is not caused. When I say "random," I mean that something is not caused AND not chosen.
Randomness is a brute fact about the universe. We are always probing to find out what really underlies a probability distribution, but whenever we pause in our labors and treat a distribution as if it were actually driven by randomness, there is nothing interesting that we can say about that randomness. Why did the coin come up heads instead of tails? I have no idea. I can wave my hand in the direction of atmospheric physics and conservation of angular momentum, but we both know that I don't have anywhere near enough information or computing power to actually calculate the path of the coin through the air.
Similarly, choice is a brute fact about the universe. When you ask me why I returned the wallet, I can wave my hand in the direction of ethics and psychology, but we both know that I don't have anywhere near enough self-understanding or computing power to actually calculate the roots of my decision in my past.
The only difference between the coin and the wallet is that I controlled the path of the wallet in a way I did not control the path of the coin. They are both "random" in the sense of being un-caused, but one is "nonrandom" in the sense of being chosen.
If I choose to return a wallet, that is just a brute fact about the universe.
So I made this particular argument partly because it's one of my favorites, succinct and devastating but also because going into what we know about brain science with the troll above would be useless. But lets go into it for a minute. We're far from understanding everything about the brain but we know a lot and have good reason to think that everything we do is the product of neuron firings. How the brain works (making choices and otherwise) can be complicated but it is almost ...
A monthly thread for posting rationality-related quotes you've seen recently (or had stored in your quotesfile for ages).
ETA: It would seem that rationality quotes are no longer desired. After several days this thread stands voted into the negatives. Wolud whoever chose to to downvote this below 0 would care to express their disapproval of the regular quotes tradition more explicitly? Or perhaps they may like to browse around for some alternative posts that they could downvote instead of this one? Or, since we're in the business of quotation, they could "come on if they think they're hard enough!"