Aether (classical element) in the context of "Ichor"

Aristotelian physics is the form of natural philosophy described in the works of the Greek philosopher Aristotle (384–322 BC). In his work Physics, Aristotle intended to establish general principles of change that govern all natural bodies, both living and inanimate, celestial and terrestrial – including all motion (change with respect to place), quantitative change (change with respect to size or number), qualitative change, and substantial change ("coming to be" [coming into existence, 'generation'] or "passing away" [no longer existing, 'corruption']). To Aristotle, 'physics' was a broad field including subjects which would now be called the philosophy of mind, sensory experience, memory, anatomy and biology. It constitutes the foundation of the thought underlying many of his works.

Key concepts of Aristotelian physics include the structuring of the cosmos into concentric spheres, with the Earth at the centre and celestial spheres around it. The terrestrial sphere was made of four elements, namely earth, air, fire, and water, subject to change and decay. The celestial spheres were made of a fifth element, an unchangeable aether. Objects made of these elements have natural motions: those of earth and water tend to fall; those of air and fire, to rise. The speed of such motion depends on their weights and the density of the medium. Aristotle argued that a vacuum could not exist as speeds would become infinite.

The classical elements typically refer to earth, water, fire, air, and (later) aether which were proposed to explain the nature and complexity of all matter in terms of simpler substances. Ancient cultures in Greece, Angola, Tibet, India, and Mali had similar lists which sometimes referred, in local languages, to "air" as "wind", and to "aether" as "space".

These different cultures and even individual philosophers had widely varying explanations concerning their attributes and how they related to observable phenomena as well as cosmology. Sometimes these theories overlapped with mythology and were personified in deities. Some of these interpretations included atomism (the idea of very small, indivisible portions of matter), but other interpretations considered the elements to be divisible into infinitely small pieces without changing their nature.

The celestial spheres, or celestial orbs, were the fundamental entities of the cosmological models developed by Plato, Eudoxus, Aristotle, Ptolemy, Copernicus, and others. In these celestial models, the apparent motions of the fixed stars and planets are accounted for by treating them as embedded in rotating spheres made of an aetherial, transparent fifth element (quintessence), like gems set in orbs. Since it was believed that the fixed stars were unchanging in their positions relative to one another, it was argued that they must be on the surface of a single starry sphere.

In Aristotelian physics and Greek astronomy, the sublunary sphere is the region of the geocentric cosmos below the Moon, consisting of the four classical elements: earth, water, air, and fire.

The sublunary sphere was the realm of changing nature. Beginning with the Moon, up to the limits of the universe, everything (to classical astronomy) was permanent, regular and unchanging—the region of aether where the planets and stars are located. Only in the sublunary sphere did the powers of physics hold sway.

The microcosm–macrocosm analogy (or, equivalently, macrocosm–microcosm analogy) refers to a historical view that posited a structural similarity between the human being (the microcosm, i.e., the small order or the small universe) and the cosmos as a whole (the macrocosm, i.e., the great order or the great universe). Given this fundamental analogy, truths about the nature of the cosmos as a whole may be inferred from truths about human nature, and vice versa.

One important corollary of this view is that the cosmos as a whole may be considered to be alive, and thus to have a mind or soul (the world soul), a position advanced by Plato in his Timaeus. Moreover, this cosmic mind or soul was often thought to be divine, most notably by the Stoics and those who were influenced by them, such as the authors of the Hermetica. Hence, it was sometimes inferred that the human mind or soul was divine in nature as well.

Incorporeality is "the state or quality of being incorporeal or bodiless; immateriality; incorporealism." Incorporeal (Greek: ἀσώματος) means "Not composed of matter; having no material existence."

Incorporeality is a quality of souls, spirits, and God in many religions, including the currently major denominations and schools of Judaism, Christianity, Islam, and the Baháʼí Faith. In ancient philosophy, any attenuated "thin" matter such as air, aether, fire or light was considered incorporeal. The ancient Greeks believed air, as opposed to solid earth, to be incorporeal, insofar as it is less resistant to movement; and the ancient Persians believed fire to be incorporeal in that every soul was said to be produced from it. In modern philosophy, a distinction between the incorporeal and immaterial is not necessarily maintained: a body is described as incorporeal if it is not made out of matter.