 For another example—and here, in the applicability of his schema to widely divergent registers, is one of the aspects of Deleuze as metaphysician—let us try to construct the Idea of hurricanes. The differential elements would be material “flows” driven by intensive differences in temperature and pressure but undetermined in form (neither smooth nor turbulent, neither big nor small) and function (neither forming nor destroying of weather events). These flows qua differential elements enter into relations of reciprocal determination linking changes in any one element to changes in the others; thus temperature and pressure differences will link changes in air and water currents to each other: updrafts are related to downdrafts even if the exact relations (the tightness of the links, the velocity of the flows) are not yet determined. Finally, at singular points in these relations singularities are determined that mark qualitative shifts in the system, such as the formation of thunderstorm cells, the eye wall, and so on. But this is still the virtual Idea of hurricanes; real existent hurricanes will have measurable values of these variables so that we can move from the philosophical realm of sufficient reason to that of scientific causation. A hurricane is explained by its Idea, but it is caused by real wind currents driven by real temperature supplied by the sun to tropical waters.