Aristotle believed that there could be no base unit of matter. He argued against the existence of the atom. Aristotle's theory has been proven incorrect. Both Democritus's and Aristotle's theories were developed around the same time around 400 and 300 B.C. during the era of ancient Greek philosophy. He demonstrated the formation of water in a sealed container by combining hydrogen and oxygen, showing water to be a compound instead of an indivisible element, as had been previously believed. 450 B.C. Aristotle did not believe in the atomic theory and he taught so otherwise. He thought that all materials on Earth were not made of atoms, but of the four elements, Earth, Fire, Water, and Air. He believed all substances were made of small amounts of these four elements of matter. Believed atoms were mechanically bound. Aristotle: He rejected Democritus atomic theroy and didn't think atoms move through empty spaces because he didn't think that empty spaces existed. He believed that all matter consisted of four elements. In 1897, English physicist J. J. Thomson (1856–1940) disproved Dalton's idea that atoms are indivisible. When elements were excited by an electrical current, atoms break down into two parts. One of those parts is a negative tiny particle, which Thomson called a corpuscle in 1881. As the father of western logic, Aristotle was the first to develop a formal system for reasoning. He observed that the deductive validity of any argument can be determined by its structure rather than its content, for example, in the syllogism: All men are mortal; Socrates is a man; therefore, Socrates is mortal.