One of the central concepts in phenomenology is that consciousness is characterized by intentionality. This concept has a long history, and it continues to play a central role in philosophical considerations right up to the present day. Husserl appropriates this concept from Brentano, who in turn finds it in medieval philosophy. The medieval philosophers trace it back to Aristotle, who claims to be explicating a saying from Empedocles: "Like is known by like' (homoia homoiois gignôsketei).