Greek physiology The concept of motion is closely related to the idea of change, and it is arguments about what made change possible that led the early Greek philosophers to pioneer naturalistic explanations for phenomena.
Heraclitus (born circa 535 BC) had famously declared that "all things are in motion like a stream".
Motion only a perception Parmenides (born circa 475 BC) and his followers held that
motion is only perceived but cannot actually exist. He professed that from our human point of view there are two aspects to the study of the universe of which we must be aware, on the one hand how we see it, and on the other how it must really be. Motion is a fact from our point of view, but Parmenides argues that as far as things must really be, it is logically impossible that motion could exist as we perceive it.
Zeno of Elea, a pupil of Parmenides, formulated the Arguments against motion, more commonly referred to as the
paradoxes, in order to support his master's theories of the One and of the consequent impossibility of motion at the fundamental level. The rigorous denial of even the possibility of motion forced a more thorough response from philosophers engaged on the same theoretical project. This school of thought leaned on the notion of infinite continuous matter, space (and time).
Atomism and determinism In response to Parmenides definition of motion,
Democritus (born circa 460) expounded the
atomic theory, in which indivisible bits of matter are in constant motion through the void. In the absence of something to perturb them they fall evenly through space. According to this school of thought matter and or space (and time) are discrete and finite. Evidence for this theory was found by
John Dalton in the early 1800s, explaining the finding that chemical decomposition of compounds gives whole numbered ratios of weight, leading to
Dalton's atomic theory Motion conceived in this way led to the approach of
determinism and therefore to questioning how
free will could exist. In response,
Epicurus appears to have included the concept of the
clinamen, or atomic swerve. This tiny random motion serves to bring atoms into contact and begin the cascade that leads to the organization of matter as it is perceived by us, introducing an element of uncertainty allowing for the existence of individual choice, an essential concept in Epicure's philosophy.
Plato and Aristotle According to
Plato (circa 425 BC), motion is a phenomenon that can never be completely comprehended or described. It originates in infinite and continuous "spiritual" self-motion which is synonymous to life and to the soul. This perpetual motion causes "communicated" motion, which is the perceived motion of bodies.
Aristotle (384 BC) claimed that all motion is caused, and can be sensed, but originally was
potentially present in the now moving body. Once there is motion, that motion will continue infinitely unless it is stopped. ==Medieval==