I’ve always found it interesting to revisit some of the theories of the ancients and compare them to our modern scientific concepts regarding matter. From earliest times, philosophers in particular have stated their a priori opinions about the composition of the “stuff” that gives reality to our everyday world.
Yet, the basic conception of atomic particle physics dates back to 500 B.C. when the Greek philosopher Leucippus and his pupil Democritus suggested that matter consists of small, indivisible particles they called atoms. For more than 2000 years after this, the notion of atoms lay in obscurity. For many centuries, people believed that all matter consisted of four elements: Earth, Fire, Air, and Water. These elements existed in an Aether or as we might call it space.
Aristotle, believed in these elements but he was deeply interested in how they come together to make up the outside world of reality. With little equipment of any kind, Aristotle examined nature as best he could by sheer contemplation. With his mind he examined various kinds of things—chairs, cats, women, water, the earth itself. He decided that there were critical attributes common to all these items. He categorized these attributes—substance, quantity, quality, relation, place, time, position, state, action, affection. [Aristotle Physics (Oxford Classics)]
However, he noticed that the category of substance was by far the most critical. Unless matter had substance, none of the other attributes could exist. Substance was somehow different from the rest. Quantity depended on substance for existence. One could not hold an apple, or several apples for that matter, unless the apples first had substance.
Quality depended on substance. Apples could not be tasty or rotten, red or green unless they first had substance. These accidentals like tastiness and color and size could not exist by themselves. Greenness could not be held in hand. It first had to exist in a thing. Likewise, relation, place, and the other five categories were meaningless unless they first existed in some substance.
But then Aristotle reasoned that a cat had substance, but a cat was surely different from a person; a rock had substance but rocks were totally different from plants; and although it couldn’t be seen, air had substance but was vastly different from water. He searched his mind for the essential factor that made one substance differ from another.