Prior to introducing the term "holon" itself, Koestler articulated the concept in "The Act of Creation" (1964), in which he refers to the relationship between the searches for subjective and objective knowledge:Einstein's space is no closer to reality than Van Gogh's sky. The glory of science is not in a truth more absolute than the truth of Bach or Tolstoy, but in the act of creation itself. The scientist's discoveries impose his own order on chaos, as the composer or painter imposes his; an order that always refers to limited aspects of reality, and is based on the observer's frame of reference, which differs from period to period as a Rembrant nude differs from a nude by Manet.Koestler would finally propose the term "holon" in "The Ghost in the Machine" (1967), using it to describe natural organisms as composed of semi-autonomous sub-wholes (or, parts) that are linked in a form of hierarchy, a "holarchy", to form a whole. The title of the book itself points to the notion that the entire 'machine' of life and of the universe itself is ever-evolving toward more and more complex states, as if a ghost were operating the machine.