Solipsists think they are unjustified in believing in a world external to their minds, as one only ever knows one’s own mind and there is no obvious reason the patterns in it should be driven by something else (curiously, holding such a position does not entirely dissuade people from trying to convince others of it). This can then be debated on grounds of whether a single mind imagining the world is more or less complex than a world causing such a mind to imagine a world.
The problem of other minds is that even if you believe in the outside world that you can see, you can’t see other minds. Most of the evidence for them is by analogy to yourself, which is only one ambiguous data point (should I infer that all humans are probably conscious? All things? All girls? All rooms at night time?).
SIA says many minds are more likely than one, given that you exist. Imagine you are wondering whether this is World 1, with a single mind among billions of zombies, or World 2, with billions of conscious minds. If you start off roughly uncertain, updating on your own conscious existence with SIA shifts the probability of world 2 to billions of times the probability of world 1.
Similarly for solipsism. Other minds probably exist. From this you may conclude the world around them does too, or just that your vat isn’t the only one.
SIA on other minds
Another interesting implication if the self indication assumption (SIA) is right is that solipsism is much less likely correct than you previously thought, and relatedly the problem of other minds is less problematic.
Solipsists think they are unjustified in believing in a world external to their minds, as one only ever knows one’s own mind and there is no obvious reason the patterns in it should be driven by something else (curiously, holding such a position does not entirely dissuade people from trying to convince others of it). This can then be debated on grounds of whether a single mind imagining the world is more or less complex than a world causing such a mind to imagine a world.
The problem of other minds is that even if you believe in the outside world that you can see, you can’t see other minds. Most of the evidence for them is by analogy to yourself, which is only one ambiguous data point (should I infer that all humans are probably conscious? All things? All girls? All rooms at night time?).
SIA says many minds are more likely than one, given that you exist. Imagine you are wondering whether this is World 1, with a single mind among billions of zombies, or World 2, with billions of conscious minds. If you start off roughly uncertain, updating on your own conscious existence with SIA shifts the probability of world 2 to billions of times the probability of world 1.
Similarly for solipsism. Other minds probably exist. From this you may conclude the world around them does too, or just that your vat isn’t the only one.