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 and Nothingness of metaphysics which denies or refuses grace inevitably ends by setting up in front of us the image of an atrophied and contradictory world where the better part of ourselves is finally unable to recognise itself." The philosopher Jean Wahl criticized Sartre's arguments about the topic of "nothing". The philosopher Frederick Copleston, writing in "A History of Philosophy" (1946–1986), described Sartre's view that all human actions are the result of free choice as "highly implausible", though he noted that Sartre had ways of defending his position. The British philosopher A.J. Ayer said that, apart from some psychological insights, the book