Being and Time raises the problem of "authenticity," that is, the potentiality or otherwise for mortal "Dasein" to exist "fully" enough that it might actually understand being. Heidegger is clear throughout the book that nothing makes certain that "Dasein" is capable of this understanding. Finally, this question of the authenticity of individual "Dasein" cannot be separated from the "historicality" of "Dasein". On the one hand, "Dasein", as mortal, is "stretched along" between birth and death, and thrown into its world, that is, thrown into its "possibilities", possibilities which "Dasein" is charged with the task of assuming. On the other hand, "Dasein's" access to
Being eventually entail the shortening and lengthening of time as well which has never been observed. This logical objection, which was made on Aristotle's argumentation, could not be answered in the ancient times or medieval age, but now it does not sound contradictory to the real nature of Time (as addressed in relativity theory), so by a reverse argument, a philosopher may indeed deduce that everything is changing (moving) even in the deepest core of Being. Although innovated in the late medieval period, Thomism was dogmatized in the Renaissance. From roughly 1277 to 1567, it dominated the philosophic landscape. The rationalist