Assertive and non-Assertive Sentences. Classifications of the ’oratio perfecta’ in the Thirteenth Century

Since logic in the 13th century is focussed on syllogistics as its main subject, textbooks on logic provide us with large and detailed treatments of the proposition as the immediate and constitutive basis of the syllogism. In the present paper I will give a survey of these treatments and pay special attention to a certain side-issue, namely to non-assertive sentences and to some difficulties concerning their classification. I will focus on William of Sherwood's apporach to the subject and compare it with the conceptions of Roger Bacon, Peter of Spain and Lambert of Lagny, who are the auhtors of the three main logic compendia besides William of Sherwood's in the thirteenth century.