Doubt (n.) is that which we must have grounds for just as we do for belief. We do not have grounds to doubt 'I know I have a brain'.
Doubt (n.) is recognized in a stranger's language largely by gestures, the play of the face, and the tone of voice.
Doubt (n.) about another's cow does not require owning a cow.
Doubt (n.) belongs to a language-game, as is easily forgotten; turning an object over is its primitive root, but there is doubt only with its typical antecedents and consequences.
Doubt (n.) is possible only for someone acquainted with such a thing as a reason for doubt; a child or monkey feeling a chair all over is not doubting.
Doubt (n.) about an inner process is an expression, an instinctive form of behaviour toward someone else.
Doubt (n.) sometimes has unknown consequences and no known removal, and then it has no clear meaning.
Doubt (n.) whether a groaning sleeper is in pain is a move in an existing game, which needs criteria elsewhere; its colouring differs case by case.
Doubt (n.) can only be learnt after certain things, as miscalculation needs calculation first.
Doubt (n.) about another's pain requires not pain but the concept of pain.
Doubt (n.) and question are possible only from a standpoint from which a question is possible; we cannot ask about what makes questions possible.
Doubt (n.) repressed in a child learning arithmetic, buried by education, is what the philosopher urges to demand clarification.