Take, again, the ideas of _event_ and _cause_. The idea of an event is a _contingent_ idea; it is the idea of something which might or might not have happened. There is no impossibility or contradiction in either supposition. The idea of cause is a _necessary_ idea. An event being given, the idea of cause is necessarily implied. An uncaused event is an impossible conception. The idea of cause is also a _universal_ idea extending to all events, actual or conceivable, and affirmed by all minds. It is a rational fact, attested by universal consciousness, that we can not think of an event transpiring without a cause; of a thing being the author of its own existence; of something generated by and out of nothing. _Ex nihilo nihil_ is a universal law of thought and of things. This universal "law of causality" is clearly distinguishable from a _general_ truth reached by induction. For example, it is a very general truth that, during twenty-four hours, day is succeeded by night. But this is not a necessary truth, neither is it a universal truth. It does not extend to all known lands, as, for example, to Nova Zembla. It does not hold true of the other planets. Nor does it extend to all possible lands. We can easily conceive of lands plunged in eternal night, or rolling in eternal day. With another system of worlds, one can conceive other physics, but one can not conceive other metaphysics. It is impossible to imagine a world in which the law of causality does not reign. Here, then, we have one absolute principle (among others which may be enumerated), the existence and reality of which is revealed, not by sensation, but by reason--a principle which transcends the limits of experience, and which, in its regular and logical development, attains the knowledge of the Absolute Cause--the First Cause of all causes--God.