You remember the old satire which represents one of the old school of medical men,--one of the breed to whom medicine and logic seemed closely allied sciences,--who, asked why opium puts people to sleep, answers very sapiently "because it has a dormitive virtue." Instead of an explanation he simply transforms the premiss by the introduction of an abstraction, an abstract noun in the place of a concrete predicate. It is a poignant satire, because everyone is supposed to know well enough that this transformation from a concrete predicate to an abstract noun in an oblique case, is a mere transformation of language that leaves the thought absolutely untouched. I knew this as well as everybody else until I had arrived at that point in my analysis of the reasoning of mathematics where I found that this despised juggle of abstraction is an essential part of almost every really helpful step in mathematics; and since then what I used to know so very clear does not appear to be at all so....It is not an explanation; but it is good sound doctrine, namely that something in opium must explain the facts observed.
C. S. Peirce, Pragmatism as a Principle and Method of Right Thinking, Turrisi, ed. SUNY Press (Albany: 1997) p. 133. Catherine Legg has an excellent paper (PDF) on this argument.