The noumenon /ˈnuːmɨnɒn/ is a posited object or event that is known (if at all) without the use of the senses. The term is generally used in contrast with, or in relation to "phenomenon", which refers to anything that appears to, or is an object of, the senses. In Ancient philosophy, the noumenal realm was equated with the world of ideas known to the philosophical mind, in contrast to the phenomenal realm, which was equated with the world of sensory reality, known to the uneducated mind. 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.
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