Very abstract thinking is necessary to understand Hegel’s system, but the system itself is presented by him as a literal account of reality. Categories are at the outset literally embedded in physical nature, which expresses them. Space expresses a lower category of being, whereas living organisms embody and express the higher categories of concept, purpose, and life. Thus, the development of the system of thought is evident in the development of the real world, except that thought, or the Absolute, is the ultimately real actualizing and defining principle of everything that exists.