A mode of philosophical reasoning which holds that the only reliable source of knowledge is experience (i.e. that which can be observed). It denies that there is any knowledge outside of the realm of the observable. The main empiricist philosophers are: David Hume, John Locke, and John Stuart Mill. It therefore rejects concepts like Kant, Immanuelâs notion of the categories, which cannot be sensed directly, but whose existence must be inferred (we cannot observe the universe in its entirety, but its existence may be inferred). Kantâs entire philosophical career was directed against the empiricist philosophy and towards building an alternative, which he termed critical philosophy (the philosophical basis of critical theory). In the wake of Kant, philosophy has split into two: continental and empiricist. The former, which is Kantian or critical in outlook, is so named by the latter because it is primarily European in origin, whereas empiricism is almost exclusively British and North American (also known as analytic philosophy).