For all the credit given Jefferson as statesman, architect, and inventor, he is rarely noted in the annals of empirical science. Believing that matrices of cooccurring events would yield an understanding of the laws that governed nature, Jefferson searched for instances of combination and of the interdependence of phenomena. He maintained diaries of astronomical events, of rainfall, and of the first appearance and subsequent co-occurrence of about forty types of vegetables, using these data to speculate about “natural laws,” and, more pragmatically, to make decisions about ploughing, planting, and crop rotation.

Co-occurrence is an interesting problem for this investigation since a greater than chance probability of co-occurrence of two or more types of cultural suppliers in a large city provides an indication of either (1) organizational interdependencies, or (2) that critical masses involving substantial numbers of people share a taste for at least two types of culture.