method of isolation. In detail, however, the method pursued is unlike that of Kant in that it does not start from the knowing mind but rather from the objects of knowing. These, it is argued, show aradical division into the existential and the non-existential. Physical science deals with the former; mathe- matics and logic with the latter. In the former, some things, namely sense-data, are objects of infallible apprehension; while certain essences or subsistences, immaterial in nature because non-existential and non-physical, are the subjects of an equally assured cognition by reason. Uncertainty appertains only to combinations of ultimate and simple objects, combinations formed in reflective thought. As long as we stick to the self- guaranteed objects, whether of sense or of pure intellect, there is no opening for any uncertainty or any risk.