I can put myself in the position of relating some external symbols to some internal events, for example, moaning and contortion of the face to the feeling of pain. I know from my pain experience that when I feel pain, I tend to moan and contort my face. So as soon as I see other people with the same external symbols, I take it for granted that they have the same internal events as I do. After all, I and others are obviously similar in behavior and general physical function
Similar results must have similar causes.
why not also in inner activity.