Platon & Aristotle
In the Aristotelian scheme, noös is the basic understanding or consciousness that enables human beings to think rationally.
In early Greek usage, Homer used noös to mean the mental activities of mortals and immortals, such as what they really have in mind as opposed to what they say aloud. For Aristotle, this was distinct from processing sensory perception, including the use of imagination and memory, which other animals can do. This therefore links the discussion of noos to the discussion of how the human mind defines definitions in a coherent and communicable way, and whether people should be born with an innate potential to understand the same universal categories of the same logical way. Deriving from this, it has also sometimes been held, particularly in classical and medieval philosophy, that individual noös must need help of a spiritual and divine type.
Plato used the word noös in many ways that were not unusual in contemporary Greek, and often simply meant "common sense" or "conscience". It was one of many words related to thought, thought and perception with the mind. Regarding the Noös which are the source of understanding for individuals, Plato is widely known to have used ideas from Parmenides in addition to Anaxagoras.