Professor Murray Gell-Mann told us how, in 1963, in a submission to Physics Letters, he “employed the term ‘mathematical’ for quarks that would not emerge singly and ‘real’ for quarks that would.” Three years later he offered an improved “characterization of mathematical quarks by describing them in terms of the limit of an infinite potential, essentially the way confinement is regarded today. Thus what I meant by ‘mathematical’ for quarks is what is now generally thought to be both true and predicted by QCD.” But in using the term “mathematical” Professor Gell-Mann got himself into some hot water, for “up to the present, numerous authors keep stating or implying that when I wrote that quarks were likely to be ‘mathematical’ and unlikely to be ‘real,’ I meant that they somehow weren't there. Of course, I meant nothing of the kind.”

How did Gell-Mann get himself into this little predicament? “I did not want to call [confined] quarks ‘real’ because I wanted to avoid painful arguments with philosophers about the reality of permanently confined objects. In view of the widespread misunderstanding of my carefully explained notation, I should probably have ignored the philosopher problem and used different words.”

At the conference Gell-Mann told us about the doctor's prescription he kept posted in his office admonishing him not to debate philosophers, suggesting that his choice of the word “mathematical” was his effort to follow the prescription.