Final answer:
Philippe Pinel did not argue that the mentally ill were possessed by demons. He advocated for humane treatment of the mentally ill and believed that mental illness was a result of physical and environmental factors.
Step-by-step explanation:
Philippe Pinel did not argue that the mentally ill were possessed by demons. This is false. Pinel was a key figure in the development of modern psychiatry and he advocated for humane treatment of the mentally ill. He believed that mental illness was a result of physical and environmental factors, not demonic possession. Pinel is known for his efforts to reform the treatment of mental illness in the late 18th and early 19th centuries.