whose complete cognition, to which in the end all a priori principles must come down to, is only possible experience, and consequently those prin ciples can have as their goal nothing but the conditions of the unity of empirical cognition in the synthesis of the appearances; but these conditions are thought only in the schema of the pure concept of the under standing, and the category contains the function, unrestricted by any sensible condition, of their unity, as of a synthesis in general.