 In emphasizing that only matter can instantiate the concept of substance here, Kant is alluding to the way in which the conservation of the total quantity of matter, in the Metaphysical Foundations, realizes the (transcendental) principle of the conservation of  substance.[43]  Moreover, Kant’s language at B277–278 (we “undertake [vornehmen]” time determination by observing “motion of the sun with respect to objects on the earth”) thereby suggests a progressive empirical procedure in which we begin with our perspective here on earth, measure the duration of time by the apparent motion of the sun, and then proceed to correct this measure in light of our evolving astronomical  knowledge.[44]