In the Critique of Pure
Kant distinguished between objects as phenomena, which are objects as shaped and grasped by
human sensibility and understanding, and objects as things-in-themselves or noumena, which do not appear to us
in space and time and about which we can make no legitimate judgments.
The noumenon is knowledge of an object or event
without the use of the senses. Noumenon’s opposite is ‘phenomenon’ – knowledge from use of the
In Ancient philosophy, the noumenal realm was
equated with the world of ideas known to the philosophical mind (eg, Plato’s
‘Forms’), in contrast to the phenomenal realm, which was equated
with the world of sensory reality (eg, Aristotle’s
Modern philosophy has generally denied the
possibility of knowledge independent of the senses, and Immanuel Kant gave this point of view its classical
version, saying that the noumenal world may exist, but it is completely
unknowable to humans. In Kantian philosophy the unknowable noumenon is often linked to the
unknowable "thing per se" (Ding an sich), although how to characterize the nature of the relationship is a
question yet open to some controversy.