One explanation of the division asks whether the proximate route to cognition comes from outside the knower or involves a capacity of the knower. Report conveys information from another source; sense uses a perceptual faculty; and reason apprehends conceptual and inferential relations.
One may see a building's height directly, hear a reliable report about it, or compare two known heights through reasoning. The subject can be the same while the route and evidential status vary. The external/internal contrast helps organize the three, but the decisive distinctions concern transmitted information, sensory apprehension, and rational judgment.