According to Theophrastus, Alcmaeon was the first Greek thinker to distinguish between sense perception and understanding and to use this distinction to separate animals, which only have sense perception, from humans, who have both sense perception and understanding (DK, B1a, A5). Alcmaeon is also the first to argue that the brain is the central organ of sensation and thought (DK, A5, A8, A10). There is no explicit evidence, however, as to what Alcmaeon meant by understanding. The word translate