 In Problems, Russell distinguished knowledge by acquaintance, which involves a direct relation to sense data, from knowledge by description or “knowledge that”. Although bare acquaintance makes us aware of the properties of sense data, it does not assert any truths or involve any judgments, hence does not constitute “knowledge that” something is the case (1912 [1997: 46]). We come to know basic facts about sense data by making judgments about them. In obtaining sense data of a brown table, we easily come to know that we are seeing something brown, or, subsequently, a whitish sheen, or an appearance of one or another trapezoidal surface. This is what Russell calls “knowledge of things by description” (1912 [1997: 46]). Description is only possible if we have access to universals, such as brownness, whiteness, being a surface, being a trapezoid, and so on. According to Russell, repeated sensations allow us to become acquainted with sensory universals: