The Sceptical Chymist or Chymico-Physical Doubts & Paradoxes is the title of Robert Boyle's masterpiece of scientific literature, published in London in 1661. In the form of a dialogue, the Sceptical Chymist presented Boyle's hypothesis that matter consisted of atoms and clusters of atoms in motion and that every phenomenon was the result of collisions of particles in motion. He appealed to chemists to experiment and asserted that experiments denied the limiting of chemical elements to only the classic four: earth, fire, air, and water. He also pleaded that chemistry should cease to be subservient to medicine or to alchemy, and rise to the status of a science. Importantly, he advocated a rigorous approach to scientific experiment: he believed all theories must be proved experimentally before being regarded as true. For these reasons Robert Boyle has been called the founder of modern chemistry.