Regarding the first type of error, an old adage tells us: "You can't compare apples with oranges." A correct process of measurement (whether cardinal or ordinal) requires comparison among attributes belonging to the same scale of measurement. For instance, we cannot measure the weight of a sofa in terms of the length of a pencil. In Section 4 we shall find that attempts at interpersonal value comparisons are similarly limited.

Another version of this error can be seen in attempts to place attributes that are different in kind on a common scale of measurement. Suppose, for example, that we attempted to designate "long" and "green" as opposites, constructing a scale of measurements as follows:

very long very green

Clearly, any "measurements" based on this scale would be arbitrary and not based on reality; we might even regard anyone who attempted them as mildly schizophrenic. The same fallacy, however, is often committed with more complex concepts, such as those associated with the ethical and political issues to be addressed in later sections.

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