The Sceptical Chymist: or Chymico-Physical Doubts & Paradoxes is the title of a book by Robert Boyle, published in London in 1661. In the form of a dialogue, the Sceptical Chymist presented Boyle's hypothesis that matter consisted of corpuscles and clusters of corpuscles in motion and that every phenomenon was the result of collisions of particles in motion. Boyle also objected to the definitions of elemental bodies propounded by Aristotle and by Paracelsus, instead defining elements as "perfectly unmingled bodies" (see below). For these reasons Robert Boyle has sometimes been called the founder of modern chemistry.