Aristotle: Aristotle of Stagira (384-322 B.C.), Greek philosopher and scientist. The son of a physician, Aristotle was a student of Plato but developed methods of inquiry different from those of his teacher. Unlike Plato, Aristotle felt that one could, and in fact must, trust one's senses in the investigation of knowledge and reality.
Aristotle's writings cover a wide variety of subjects. His treatises on human anatomy are lost, but his many works on animals advocate direct observation and anatomical comparisons between species through dissection. Aristotle set the stage for what would be the scientific method.
Aristotle taught early (now known to be incorrect) concepts that life arises by spontaneous generation, semen is superfluous, the seat of consciousness is in the heart, and disease is due to imbalance between the four humors.