Freedom in the practical sense is the independence of the power of choice from necessitation by impulses of sensibility
Immanuel KantUpon the solution of this problem, or upon sufficient proof of the impossibility of synthetical knowledge a priori, depends the existence or downfall of metaphysics.
Immanuel KantOur knowledge springs from two fundamental sources of the mind; the first is the capacity of receiving representations (receptivity for impressions), the second is the power of knowing an object through these representations (spontaneity [in the production] of concepts).
Immanuel Kant