 They draw a distinction between patterns, which are observed, and processes, which may be inferred from patterns, but which should not be presupposed.Before the emergence of cladistics as a school, Joseph Henry Woodger criticized phylogenetic systematics on the grounds that homology by way of common ancestry is "putting the cart before the horse, because descent from a common ancestor is something assumed, not observed.It belongs to theory, whereas morphological correspondence is observed.