In early Greek uses, Homer used "nous" to signify mental activities of both mortals and immortals, for example what they really have on their mind as opposed to what they say aloud. It was one of several words related to thought, thinking, and perceiving with the mind. In pre-Socratic philosophy, it became increasingly distinguished as a source of knowledge and reasoning opposed to mere sense perception or thinking influenced by the body such as emotion. For example, Heraclitus complained that "much learning does not teach "nous"".