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 ‘Particulars’).
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.