 The doctrine of secondary intelligibles cut down the number of subjects treated within the logic treatises, or at least, treated as strictly logical subjects, and the doctrine of dividing knowledge into conception and assent determined the structure of what was left in Avicennan logic treatises. Formal interests of post-Avicennan logicians further limited interest in demonstration; syllogistic, for example, became a central focus of research from the thirteenth century on. Further changes were introduced for clarity of exposition.