causality may be itself the effect of a non-empirical and intelligible causality—its connection with natural causes remaining nevertheless intact? Such a causality would be considered, in reference to phenomena, as the primal action of a cause, which is in so far, therefore, not phenomenal, but, by reason of this faculty or power, intelligible; although it must, at the same time, as a link in the chain of nature, be regarded as belonging to the sensuous world.
A belief in the reciprocal causality of phenomena is necessary, if we are required to look for and to present the natural conditions of natural events, that is to say, their causes. This being admitted as unexceptionably valid, the requirements of the understanding, which recognizes nothing but nature in the region of phenomena, are satisfied, and our physical explanations of physical phenomena may proceed in their regular course, without hindrance and without opposition. But it is no stumbling-block in the way, even assuming the idea to be a pure fiction, to admit that there are some natural causes in the possession of a faculty which is not empirical, but intelligible, inasmuch as it is not determined to action by empirical conditions, but purely and solely upon grounds brought forward by the understanding—this action being still, when the cause is phenomenized, in perfect accordance with the laws of empirical causality. Thus the acting subject, as a causal phenomenon, would continue to preserve a complete connection with nature and natural conditions; and the phenomenon only of the subject (with all its phenomenal causality) would contain certain conditions, which, if we ascend from the empirical to the transcendental object, must necessarily be regarded as intelligible. For, if we attend, in our inquiries with regard to causes in the world of phenomena, to the directions of nature alone, we need not trouble ourselves about the relation in which the transcendental subject, which is completely unknown to us, stands to these phenomena and their connection in nature. The intelligible ground of phenomena in this subject does not concern empirical questions. It has to do only with pure thought; and, although the effects of this thought and action of the pure understanding are discoverable in phenomena, these phenomena must nevertheless be capable of a full and complete explanation, upon purely physical grounds and in accordance with natural laws. And in this
