section_path: History of atomic theory/In philosophy
section_name: In philosophy
paragraph_text: In philosophy
  
  The basic idea that matter is made up of tiny indivisible particles is an old idea that appeared in many ancient cultures. The word atom is derived from the ancient Greek word atomos, which means "uncuttable". But this ancient idea was based in philosophical reasoning rather than scientific reasoning. Modern atomic theory is not based on these old concepts. In the early 19th century, the scientist John Dalton (1766–1844) found evidence that matter really is composed of discrete units, and so applied the word atom to those units.