  In their attempt to clarify the way in which we should think of such principles, both the Southwestern and the Marburg Neo-Kantians reject any kind of psychological reading, which dominated among early 19th Century interpretations of Kant. The a priori principles of valid thinking are not mere facts about human psychology; they do not describe merely how our mind happens to function. Their validity is objective, that is, it is part of the formal structure of the objects of investigation and not merely an extrinsic mental scheme that exemplars of the species homo sapiens contingently apply to them.