For Schopenhauer, understanding the world as will leads to ethical concerns (see the ethics section below for further detail), which he explores in the Fourth Book of "The World as Will and Representation" and again in his two prize essays on ethics, "On the Freedom of the Will" and "On the Basis of Morality". No individual human actions are free, Schopenhauer argues, because they are events in the world of appearance and thus are subject to the principle of sufficient reason: a person's actions are a necessary consequence of motives and the given character of the individual human. Necessity extends to the actions of human beings just as it does to every other appearance, and thus we cannot speak of freedom of individual willing. Albert Einstein quoted the Schopenhauerian idea that "a man can "do" as he will, but not "will" as he will." Yet the will as thing in itself is free, as it exists beyond the realm of representation and thus is not constrained by any of the forms of necessity that are part of the principle of sufficient reason.