Although its proper opposite is 'impure', Kant normally opposes 'pure' to 'empirical'. A statement or item of knowledge which is known to be true because of its connection with some intuition. The closest we can get to gaining knowledge of the transcendent realm is to think about it by means of ideas. It is a special type of philosophical knowledge, concerned with the necessary conditions for the possibility of experience. However, Kant believes all knowing subjects assume certain transcendental truths, whether or not they are aware of it.
Every event has a cause' is a typical transcendental statement.