Doubt is a multifaceted state of mind. It can signify the end of a belief, but it can also lead to a new belief. Doubt eliminates any certainty. In extreme cases, it can be seen as skepticism, a kind of inverted belief. In small doses, doubt stimulates thinking; in excessively large doses, it paralyzes it. As an intellectual experience, doubt is one of pure pleasures; as a moral experience, it is a torment. Together with curiosity, doubt is the cradle of research, and consequently, the cradle of all systematic thinking. In small amounts, doubt kills curiosity and ends all knowledge. A treatise from the Brazilian era, which can be regarded as a philosophical foundation for Flusser's later theories on photography and media.