I begin with a tribute to a great physicist who taught me how to think about quarks and physics in general, John Bardeen. A few sentences from John could often teach you more and give more deep insight than ten hours of lectures from almost anyone else. In 1966 when I began to take quarks seriously, I was unknowingly thinking about them in the language I had learned from John during two years at the University of Illinois, as quasi-particle degrees of freedom describing the low-lying elementary excitations of hadronic matter. Unfortunately I did not realize how much my own thinking had been influenced by John Bardeen until he was gone. I dedicate this paper to his memory.

Were quarks real? Quarks as real as Cooper pairs would have been enough. Quarks leading to anything remotely approaching the exciting physics of the BCS theory would have been more than enough. John always emphasized that Cooper pairs were not bosons, and that super-conductivity was not Bose condensation. The physics was all in the difference between Cooper pairs and bosons. I was not disturbed when quarks did not behave according to the establishment criteria for particles. The physics might all be in the difference between quarks and normal particles. One had to explore the physics and see where the quark model led.

The arguments of the BCS critics that the theory was not gauge invariant did not disturb John; he knew where the right physics was.