In his treatment of the human soul, al-Farabi draws on a basic Aristotelian outline, which is informed by the commentaries of later Greek thinkers. He says it is composed of four faculties: The appetitive (the desire for, or aversion to an object of sense), the sensitive (the perception by the senses of corporeal substances), the imaginative (the faculty which retains images of sensible objects after they have been perceived, and then separates and combines them for a number of ends), and the rational, which is the faculty of intellection. It is the last of these which is unique to human beings and distinguishes them from plants and animals. It is also the only part of the soul to survive the death of the body. Noticeably absent from these scheme are internal senses, such as common sense, which would be discussed by later philosophers such as Avicenna and Averroes.