Prisoners in jails are often given numbers and are "known" by the numbers assigned. It has not yet occurred to any one that these numbers are the real prisoners, and that there is always aduplicate real object jone a number, and the other aflesh and blood person, and that these two editions of reality have to be reconciled. It is true that the numbers which constitute by means of measurements the object of scientific thought are not assigned so arbitrarily as those of prisoners, but there is no difference in philosophical principle.