Parts of foregoing chapters will have pressed too close to the rocky ground of detailed medieval scholarship for the comfort of some readers; this Conclusion, on the other hand, may seem to go up to an unpleasantly high altitude of abstraction. There is a reason: Medieval Religious Rationalities shares a common structure with its more theoretical and comparative sister volume Rationalities in History. The aim of this final section is to resume the main themes of the present book in such a way as to bring out the line of argument that the two volumes share.

Both books distinguish different ways of reasoning in order to establish the relations between them: which is symbiotic rather than antithetical. The most fundamental distinction is between conviction rationality, also called value rationality, and instrumental rationality. Both kinds of thinking can be called ‘rational’. With both, generalities as well as specificities are involved – principles and abstractions are part of our concept of rationality; and in both cases the reasons for thinking and acting held before the mind are also the actual causes of the thoughts or actions. Actions are irrational insofar as the causes of thoughts or actions are different from the reasons for them. It is crucial not to confuse irrational thoughts and actions with convictions, which, however reprehensible we may find them, fit the category of value rationality. The present book tries to discover how values and instrumental calculation affect each other, and to illustrate these relations in detail with medieval examples.