Few great medieval buildings are homogeneous, since they are the work of many generations of artists. This is widely recognized by historians, although theoreticians of culture have innocently pointed to the conglomerate cathedral of Chartres as a model of stylistic unity, in contrast to the heterogeneous character of stylelessness of the arts of modern society. In the past it was not felt necessary to restore a damaged work or to complete an unfinished one in the style of the original. Hence the strange juxtapositions of styles within some medieval objects. It should be said, however, that some styles, by virtue of their open, irregular forms, can tolerate the unfinished and heterogeneous better than others.
--Meyer Schapiro, “Style.” The Problem of Style (Fawcett Publications, 1966) edited by J.V. Cunningham.