During the period of the Roman Empire and the Middle Ages, philosophers elaborated on the existing conception of anger, many of whom did not make major contributions to the concept. For example, many medieval philosophers such as Ibn Sina (Avicenna), Roger Bacon and Thomas Aquinas agreed with ancient philosophers that animals cannot become angry. On the other hand, al-Ghazali (Algazel), who often disagreed with Aristotle and Ibn Sina on many issues, argued that animals do possess anger as one of the three "powers" in their heart, the other two being appetite and impulse. He also argued that animal will is "conditioned by anger and appetite" in contrast to human will which is "conditioned by the intellect". A common medieval belief was that those prone to anger had an excess of yellow bile or choler (hence the word "choleric"). This belief was related to Seneca's belief that "red-haired and red-faced people are hot-tempered because of excessive hot and dry humors".