THOSE who are interested in geography as a subject to be expounded educationally must welcome every approach to it which may add to its effective rationalization and bond it into the main structure of knowledge. This is not a mere teaching device, for it may make teaching more difficult, if it is to make it more effective. It makes teaching more difficult if we have to go beyond the immediate neighbour in causation, to reach basic causation and fundamental reasons. ‘To explain a geographical condition by an economic condition is immediate, but not fundamental. Some theory of economic action is implied, though it may be conveniently left unexamined and unexpressed?taken for granted. All such single economico-geographic couplets of facts taken together must ultimately conform to some theoretic principle, and have some common thread. If they do not, then there is no uniformity of causation, and no economic, still less geographical science. An economic explanation of a geographic fact is then no ‘explanation5 at all. The kind of theory which geography may involve, or which may aid geographic understanding, and help to make geography, already culturally basic to so many mental disciplines, a fully rounded science, is therefore the subject of this address.