Greek philosopher Aristotle (384–322 B.C.E.) tried to use logic to build a diagram of living things, but he realized that living things could not be so easily separated. Instead, he constructed a “ladder of nature” or “scale of perfection,” which began with humans at one end and proceeded through animals and plants to minerals at the other end. Aristotle ranked these groups on a scale based on the four classical elements: fire, water, earth, and air.