The principle of causality

In Fourfold Root of the Principle of Sufficient Reason Schopenhauer proved – in accordance with Kant and against Hume – that causality is present in the perceivable reality as its principle, i.e. it precedes and enables human perception (so called apriority of the principle of causality), and thus it is not just an observation of something likely, statistically frequent, which however does not happen "on principle" (empiricism of the principle of causality). More on this dispute in philosophy can be found in the article on free will.