You probably read my answer about Schopenhauer's will given to Wang. Schopenhauer distinguishes
between a realm of manifestation evident to the senses and that realm which is the source of
manifestation, out of which phenomena show themselves as what they are. The realm of all things is
like a circumference which is drawn around the will which is the primal source of all things; the Being
of beings. "The world is only the mirror of this willing." (World as Will and RepresentationIV.63). The
world empiricists call 'real' Schopenhauer calls 'representation'. The real world is the essence of
representation, which is the will. "The presentis the only place where the will manifests itself" (WWR
IV.54 His underscore). So you see, the will is a theory of the nature of being and time.
Did his notion of will change as time passed? Not really. Schopenhauer lived between the years 1788
and 1860. The World as Will and Representation(Der Welt als Wille und Vorstellung) his
masterpiece, came out in 1818. It is an intuitive theory and Schopenhauer expects his reader be
intuitive as well. Everything he wrote afterward is based on it and backs up what he thought then. The
main thing he wrote before, his doctoral thesis, was entitled, On the Fourfold Root of Sufficient
Reason.This rigorous work is very much a precursor to The World as Will and Representation,
working out, as it does, some of the conceptual underpinning which gives rise, for Schopenhauer, to
the 'practicality' of the distinction between what he would come to see as will and representation.