urner's frontier thesis and Mackinder's heartland thesis are examples of closed-space thinking. Closed-space theories were current at the beginning of this century when public debate was penetrated both by biology and by geography. This conjuncture allowed spatial concepts to form the basis for the theoretical arguments advanced for political positions. The internal structure of closed-space theories allowed them to promote political conclusions, because the three central terms of those theories (environment, history, recent fundamental changes) were 'essentially contestable' and capable of interpretations which supported particular political arguments. The specific political arguments promoted by Turner and Mackinder dictated the interpretations they chose and thus the internal structure of their theories