  Thomas Aquinas argued that the highest sort of demonstration had as its middle term the real definition of the subject term (Comm. on PA II 1.9, 7, 19). This led him to claim that the fourth way in which something can be per se pertained to demonstration, since it indicates an efficient causal connection, and the minor premise will be true in a demonstration because of the efficient causal connection between the essence of the subject, as expressed in its real definition, and the attribute proven of it, making it per se in the fourth way.