“by simple bodies I mean those which possess a principle of movement in their own nature, such as fire and earth with their kinds, and whatever is akin to them.”
Thus, in Aristotle’s philosophy, the four elements (fire, air, water, earth) are “simple bodies”.
Previously, he said:
“Now a continuum is that which is divisible into parts always capable of sub- division, and a body is that which is every way divisible. A magnitude if divisible one way is a line, if two ways a surface, and if three a body.”
Thus, when Aristotle spoke of “elements”, he spoke of magnitudes that possessed three dimensions–length, width and height.
In modern science, “atoms” are said to be INDIVISIBLE, meaning that they are not what Aristotle referred to when he spoke of elements.
So, when modern people say that Aristotle identified “four elements”, but modern science now knows that there are 100+ elements, they speak falsely, for what they mean by “elements” is not what Aristotle spoke of.