‘‘The strange Story of the Concept which inaugurated Modern Theoretical Physics’’ is the title of a lecture which I delivered on the invitation of Professor Franco Selleri at the University of Bari about 20 years ago. Since Professor Selleri himself has written several interesting papers on this concept and since the centennial of the birth of modern theoretical physics will be celebrated soon, I found it appropriate to dedicate this essay, containing so far unpublished critical and historical comments on this (...) concept, to Professor Selleri on the occasion of his 70th birthday. It should be emphasized that the critical comments in this essay are not intended to question the validity of the theory initiated by this concept, a theory which in the realm of its applicability is daily corroborated by numerous experiments in high-energy laboratories all over the world. Although these critical remarks refer almost exclusively to the first publication of this theory, a publication which has been hailed as ‘‘the most important paper written in the 20th century,’’ they discuss profound problems of general importance for the study of the foundations of physics. (shrink)