A If we compare the doctrine of the soul, as the physiology of inner sense, with the doctrine of bodies, as a physiology of the objects of outer sense, then we will find that aside from the fact that in both doc trines much can be cognized empirically, there is nevertheless this re markable difference, that in the latter science much can be cognized a priori from the mere concept of an extended impenetrable being, but in the former science nothing at all can be cognized a priori from the con cept of a thinking being.