Such _is_ the world in which we live; and taking this ground I say, the world is a cosmos, it is no chaos; and noticing that being possessed of sameness is an intrinsic and inalienable feature of the world, I am inclined to add the world never was and never will be a chaos. And this, if it be true at all, is true not only in general and as it were wholesale, but in its minutest details. If there were deficiencies of this order in the unobservable details, they would not be diminished by being summed up in large and ever larger amounts; on the contrary, they would increase; they would grow in proportion. This not being the case, we have not the slightest reason to doubt that in those realms of minutest existence into which, from the grossness and the lack of precision of our organs and instruments of observation, we cannot penetrate, the same order and regularity obtains as in those regions which lie open to our investigation. In other words: From this standpoint, existence is, so to say, permeated by law throughout; every event is determined and any kind of absolute chance is excluded. Following Kant’s etymology we understand by _a posteriori_ the sensory elements, and by _a priori_ the formal elements of our experience. The queer expression “a priori” is in so far justified as formal truths (such as geometrical, arithmetical, logical rules) are formulas expressing the universal samenesses of the form of existence. They contain the laws of form in a shape that is _eindeutig bestimmt_, so that an experimenter will know them _a priori_ to be so. _A priori_ means beforehand. An experimenter knows certain things even before he makes his experiments. The _a priori_ elements of experience are by no means innate truths; nor are they the historical beginning of experience. On the contrary. In their abstract purity they appear as a very late product of man’s mental evolution. The _a priori_ systems of thought are not arbitrary constructions; they are constructions raised out of the recognition of the formal, i. e. the relational, samenesses that appear in experience. All possibilities of a certain class of relations can be exhausted and formulated in theorems. As such they can be used as references to assist in the explanation and determination of new experiences. We know some part of any new experience with which we are confronted even before we have investigated it. We know certain laws of its form, and by reference to these known laws we are enabled to reduce the unknown to the known, to analyse the process and set forth that feature of it which makes _eindeutig bestimmt_. II. THE SCOPE OF NECESSITY.