In the 17 th and 18 th centuries CE, several key events helped revive the theory that matter was made of small, indivisible particles. Because of Aristotle's great influence, Democritus's theory would have to wait almost 2,000 years before being rediscovered. Aristotle accepted the theory of Empedocles, adding his own (incorrect) idea that the four core elements could be transformed into one another. Ultimately, though, Aristotle and Plato, two of the best-known philosophers of Ancient Greece, rejected the theories of Democritus. This was a remarkable theory that attempted to explain the whole physical world in terms of a small number of ideas. Democritus theorized that atomos were specific to the material that they made up, meaning that the atomos of stone were unique to stone and different from the atomos of other materials, such as fur. He suggested that atomos were eternal and could not be destroyed. Democritus called these infinitesimally small pieces of matter atomos, meaning 'indivisible'. He reasoned that if you continued to cut the stone into smaller and smaller pieces, at some point you would reach a piece so tiny that it could no longer be divided.

Democritus knew that if you took a stone and cut it in half, each half had the same properties as the original stone. Democritus's ideas were based on reasoning rather than science, and drew on the teachings of two Greek philosophers who came before him: Leucippus and Anaxagoras. Despite these problems, Empedocles's theory was an important development in scientific thinking because it was among the first to suggest that some substances that looked like pure materials, like stone, were actually made up of a combination of different 'elements.'Ī few decades after Empedocles, Democritus (460 BCE - 370 BCE), who was also Greek, developed a new theory of matter that attempted to overcome the problems of his predecessor. For example, regardless of how many times you break a stone in half, the pieces never resemble any of the core elements of fire, air, water, or earth. Empedocles's theory was quite popular, but it had a number of problems.

Atomic theory scientists