In the development of science during the last two or three decades the possibility and necessity of a sharp distinction between form and content has become clearer and clearer, and the all-importance of structure has been more fully recognised. The gradual dawning of this truth — which has not grown into full daylight yet — seems to me to be the greatest achievement of modern epistemology.
The separation of Form and Content has a history of many centuries: at first it took a metaphysical shape in the philosophy of Aristotle; since that time the border-line between Structure and Matter has continually shifted in one direction until in our present day, the last traces of content, as it were, have been removed, and pure Form has revealed itself as the purely Logical.
Science is not a collection of factual knowledge (statements of facts), but a system of explanatory knowledge (description by Laws). The more perfect it grows, i.e. the more its propositions become logically connected, the more clearly the formal character of knowledge becomes evident even to the untrained eye: science clothes itself in mathematical garments. Although this attire is sometimes looked upon with a mixture of awe and scorn even by philosophers, the really great thinkers of all times, from Plato and Democritos to Leibniz and Kant, have always been well aware that there is no hope for philosophical analysis unless it starts from an understanding of knowledge in its strictest, i.e. in the mathematical shape.
Knowledge has reached its most advanced stage in theoretical physics, and to it we have to adress ourselves in order to understand science. (Later on we shall cast a glance at other realms of knowledge and shall see that everything remains true for them. We cannot adress ourselves to pure mathematics because — this may seem strange but is a necessary consequence of the terminology we adopted — it does not contain any genuine knowledge. It is not a science, but an instrument of science which is used to formulate scientific truths and represent properly the connections between them. It does not express anything itself, but is the purely analytical method or technique of transforming equivalent expressions into each other).
Theoretical physics, if we do not consider it in the making (although, of course, it is always in the making) but as a completed system, consists of an indefinite number of propositions called Laws of Nature: They are
