Paraphrasing N. R. Campbell (Final Report, p.
340),. we may say that measurement, in the broadest
sense, is defined as the assignment of numerals to ob-
jects or events according to rules. The fact that
numerals can be assigned under different rules leads
to different kinds of scales and different kinds of
measurement. The problem then becomes that of
making explicit (a) the various rules for the assign-
ment of numerals, (b) the mathematical properties
(or group structure) of the resulting scales, and (c)
the statistical operations applicable to measurements
made with each type of scale.
Scales are possible in the first place only because
there is a certain isomorphism between what we can
do with the aspects of objects and the properties of
the numeral series. In dealing with the aspects of
objects we invoke empirical operations for determin-
ing equality (classifying), for rank-ordering, and for
determining when differences and when ratios between
the aspects of objects are equal. The conventional
series of numnerals yields to analogous operations:
We can identify the members of a numeral series
and classify them. We know their order as given
by convention. We can determine equal differences,
as 8-6=4-2,and equal ratios, as 8/4=6/3.The
between these properties of the numeralisomorphism
series and certain empirical operations which we per-
form with objects permits the use of the series as a
model to represent aspects of the empirical world.
The type of scale achieved depends upon the char-
acter of the basic empirical operations performed.
These operations are limited ordinarily by the nature
of the thing being scaled and by our choice of pro-
cedures, but, once selected, the operations determine