 Russell’s analysis of our perception of an external world advanced in other ways. In Problems (1912: ch. 1), he had noted that we are so accustomed to judging the “real” shapes of things that we believe “that we actually see the real shapes” (1912 [1997: 10]), that is, we uncritically assume that we see the table as rectangular. But when we adopt the attitude needed to produce a drawing of the table, we may come to notice the appearances of various trapezoidal shapes. In Our Knowledge (1914a: ch. 3), Russell further analyzes this difference. His analysis depends on the relation between what is logically and psychologically primitive or else derivative. Logically primitive beliefs are those that are not logically derived via inference or construction. In order to strengthen our knowledge, we seek to align these primitive beliefs with the psychologically primitive. While having an ordinary perception of the table with its actual shape, we mistakenly believe that this experience, which has resulted from a learned psychological process, is psychologically primitive; accordingly, we also designate this perception of the table as logically primitive. Scientific psychology now offers a point that Russell had attributed to learning to draw: that what is actually psychologically primitive is the perspectival view of the table as trapezoidal (1914a: 68). Armed with this psychological finding, we endeavor to make the trapezoidal datum logically primitive; what is psychologically primitive is more secure and so provides us with “hard data” by comparison with the “soft data” of the common-sense belief about the table’s shape (1914a: 69–70). As with Mill’s apparently but not actually intuitive beliefs, before epistemological analysis many beliefs about sensory things are logically primitive, because not reached through logical derivation, and psychologically derivative, because caused by extra-logical psychological processes such as association. Upon further consideration, we favor beliefs that are both psychologically and logically primitive (1914a: 69–70) and so establish sense data as logically primitive.