phenomenon, an observable fact or event; in philosophy the definitions and uses of the term have varied. In the philosophy of Aristotle phenomena were the objects of the senses (e.g., sights and sounds), as opposed to the real objects understood by the mind. Later, phenomena were considered the observed facts and were contrasted with the theories used to explain them. Modern philosophers have used "phenomenon" to designate what is apprehended before judgment is applied. For Immanuel Kant a phenomenon was the object of experience and was the opposite of a noumenon, the thing-in-itself, to which Kant's categories did not apply.