Everyone in the Middle Ages believed -- as Aristotle had -- that the heart was the seat of intelligence.

This statement is false because it presents an oversimplified generalization. While Aristotle did believe the heart was the center of intelligence, many medieval scholars actually followed the earlier Greek physician Hippocrates and later Galen, who placed intelligence in the brain. By the Middle Ages, especially after the 12th-century rediscovery of Arabic medical texts and the work of physicians like Avicenna, the brain was widely recognized in medical and philosophical circles as the seat of cognitive functions.