  Secondly, even if the concept of heat were not incomplete or superficial, in so far as it is a concept of a natural property we have good reason to think that the empirical sciences are much better equipped to discover the nature of heat than a priori reflection. The same is true of the concept of water. In so far as this is a concept of a natural substance, the empirical sciences are far better suited to tell us the nature of this substance than a priori reflection.