The classical theory of coagulation proposed by Paul Morawitz in 1905. Many of the coagulation factors known today are not represented in this theory, and it does not explain why haemophiliacs bleed (factors VIII, IX and XI are absent from this model).

The enzyme cascade model of coagulation. This cascade does not explain why factor XII deficiency is not associated with a bleeding disorder. In addition, factors VIII and V are actually co-factors for factors IX and X respectively. The model also lacks calcium and phospholipids, which are essential requirements for coagulation.