D O C U M E N T 6 R E V I E W O F M E Y E R S O N 3 1 In this sense, Meyerson is a rationalist and not an empiricist. His thoughts are, however, also distinct from critical idealism in the Kantian sense. For we do not know a priori of any feature of the system that we are seeking that it is necessarily a part of the nature of our thought. This holds also for the forms of logic and of cau- sality. We can only ask how the system of the sciences (in its present state of devel- opment) is constituted, but not how it must be constituted. The logical fundamentals of the system as well as its structure are thus conventions (as seen from the standpoint of logic) their justification is to be found solely in the ability of the system to describe observed facts, in its unity, and in the small number of the premises that it requires.[4] Meyerson sees in relativity theory a new deductive system of physics with re- spect to previously established physics he calls it “relativism” in order to point out its novelty in a formal way. Here, he has in my opinion gone too far.[5] Relativity theory by no means claims to be a new system of physics.[6] Starting from the idea suggested by our experiences with light, inertia, and gravity that there is no physi- cally preferred state of motion (the principle of relativity), it establishes the formal principle that the equations of physics should be covariant with respect to arbitrary point transformations within four-dimensional space-time.[7] The basic laws of physics—as they were previously known—are adapted to this principle with a min- imal number of modifications. The principle of relativity or covariance principle alone would provide a much too weak foundation for constructing the edifice of theoretical physics. Thus, one could preferably speak of “physics that has been adapted to the principle of relativity” rather than of “relativism” as the new system of physics. By identifying the less assertive claims to generality of the “principle of relativity” with the much more extensive claims of “relativism,” Meyerson adopts in my opinion a not completely relevant point of view with respect to the novelty and to the claims of the theory to long-term significance. Not the theory as a whole, but instead only its adaptation to the principle of relativity is new.[8] On the other hand, the principle of relativity in itself would appear to be much more clearly justified by the character of experience than the formal structure of the the- ory that has been adapted to our current state of physical knowledge. We cannot be certain today, but we fear that the concepts of the “metric field” and of the “elec- tromagnetic field” will prove to be inadequate with respect to the facts of quantum theory.[9] But the opinion that the principle of relativity as such could be brought down by this inadequacy need hardly be considered seriously. We mention all of this only in passing.[10] For Meyerson, it was important to point out that the rational system of physics has attained the character of a logically complete deductive system to a much higher degree than previously through its ad- aptation to the principle of relativity. Meyerson does not criticize this strongly