Full Idea
But for our acquaintance with the contents of our own minds, we should be unable to imagine the minds of others, and therefore we could never arrive at the knowledge that they have minds.
Gist of Idea
If we didn't know our own minds by introspection, we couldn't know that other people have minds
Source
Bertrand Russell (Problems of Philosophy [1912], Ch. 5)
Book Reference
Russell,Bertrand: 'The Problems of Philosophy' [OUP 1995], p.27
A Reaction
Not only does this depend on the notorious 'argument from analogy', but it actually strikes me as false. If a robot observed a human to be writhing in pain, it would be mystified, until it inferred that we have minds in which we actually 'feel' damage.