 The fact of culture is not static, but dynamic. As Natorp memorably put it (1912a: 184; 1910: Ch.1, §4; 1903: 366ff), the fact is not a “factum” (a thing done) but “fieri” (becoming). Culture changes; one scientific theory replaces another. In keeping with the transcendental method, only a Newtonian could have written what Kant wrote; but the transcendental method just as emphatically requires that later transcendental philosophers rethink the doctrines of the first Critique in light of the advances in mathematics and natural science since Newton. This appreciation for the historically evolving character of culture has two consequences. First, the transcendental a priori is not absolute, but relative to the current best physical theories. Second, Marburg Neo-Kantians have an additional transcendental task that Kant himself did not fully recognize: to understand how it is possible that the changes in an area of culture can themselves be objectively valid. They want to understand the objective law or method that determines how an area of culture  changes.[11]  This emphasis on the objectivity and lawlikeness of cultural change thus introduces a check on the potential relativistic or historicist consequences of their relativizing the a priori. (Cassirer in particular develops a sophisticated theory of the a priori with both relative and absolute elements; see  section 2.3.)  This emphasis on the progressive character of culture leads the Marburg Neo-Kantians to adopt a distinctive, historical method of writing and arguing, in which systematic philosophy is not separated from the history of philosophy and the history of  culture.[12]