As an aspiring science in the nineteenth and early twentieth centuries, psychology pursued quantification. A problem was that degrees of psychological attributes were experienced only as greater than, less than, or equal to one another. They were categorised as intensive magnitudes. The meaning of this concept was shifting, from that of an attribute possessing underlying quantitative structure to that of a merely ordinal attribute . This fluidity allowed psychologists to claim that their attributes were intensive magnitudes and measurable . This (...) claim was supported by an argument that order entails quantity. As adapted by psychometricians, the argument was that if an attribute is ordered, then the differences between its degrees are quantitative and, therefore, measurable. However, in a paper ignored in psychology for six decades, the issue was resolved mathematically and the resolution implies that the psychometricians’ argument was fallacious. (shrink)