How did Arthur Schopenhauer describe the will as the underlying reality of the world?

In his seminal work, The World as Will and Idea, Arthur Schopenhauer described the will as the fundamental, underlying reality of the world, or the "thing-in-itself".12

Building on the Kantian distinction between phenomena (appearances) and noumena (things-in-themselves), Schopenhauer argued that while the world we perceive is merely a representation structured by space, time, and causality, the will is the unitary, unfathomable essence that exists beyond these constructs. He characterized the will as a quasi-mystical, aimless, and insatiable life force.12

This reality is reflected in the world through an ascending series of manifestations, ranging from the blind impulses of inorganic nature to the rationally guided actions of humans. Because the will is essentially a restless, eternal striving, Schopenhauer viewed the world as inherently filled with misery and misfortune. While the will remains inaccessible to rational thought, he believed its nature could be glimpsed through aesthetics—particularly music—or transcended through asceticism and compassion, which lead to the negation of the will to life.21