Hume’s sense of ‘Magnitude’

Real magnitude, Reid went on to note, is something that must remain the same while the object remains unchanged. Apparent magnitude, in contrast, is the sort of thing that must by its very definition vary depending only on real features of the external world: the size of the object and its distance from the observation point. Accordingly, there is no skeptical lesson to be drawn from the fact that apparent magnitude changes with changes in observation point while the real magnitude remains the same. Mounting a second objection to Hume’s argument, Reid charged that even aside from any appeal to logic, common sense would tell us that this occurrence is consistent with realism.