SL,
The definition of measurement I follow is the one on the first page of the first volume of Foundations of Measurement: the association of numbers (include characters like vectors and quaternions as well) to the attributes of some class of objects or events “in such a way that the properties of the attribute are faithfully represented as numerical properties.”
What I call a magnitude structure are concrete relations in the world (or in our perceptual and thinking operations) to which application of a measurement scale is appropriate. Where I say magnitude, some others say quantity. Same difference. By appropriate, I mean, in this context, as in my 2004 Universals and Measurement: All of the mathematical structure of the measurement scale is needed to capture the magnitude structure of concretes under consideration. It means as well that all the magnitude structure is describable in terms of the mathematical structure of the measurement scale. (As noted [12] in the paper, I take this norm from Robert Geroch’s Mathematical Physics and adapt it for our broader context.)
Some conceptions of measurement are so loose that they would rate numbers on football jerseys as a measurement, which they call nominal measurement. I exclude that under the definition of measurement as I mean in the definition above. Mere distinct individuality, and even mere individuality with mere membership, does not a magnitude structure make, at least not in my book. I’d say the concepts same, different, and membership are logically prior to the concepts magnitude or measurement. The technical analysis of the various types of measurement, the various types of scales, is cast in terms of logically prior elements of logic (such as the logical connectives and, or, . . .) and elements of set theory (such as membership). So I do not go along with Rand’s attempt to analyze connectives such as and in terms of measurement omission. But I stay with her idea that all concretes stand in magnitude relations, at least to the level of ordinal structure, with other concretes. Though I exclude the logical and set-theoretic presuppositions of measurement from the measurement-omission model, it remains with me that all concretes can be brought under some concept(s) or other under the measurement-omission model. That remainder is large and a substantive conjecture. I’m not talking about the genesis of concepts here, only possibilities of analysis of concepts (and similarity relations) in terms of measurement omission. Because of the logical priority (however might stand genetic priority) of logic and set theory in relation to theory of measurement, I approach a book aiming to analyze such things as sets in terms of measurement—as I gather, so far, is an aim in Robert Knapp’s book—with much wariness.
SL, I’ll have to pass on physical magnitude structures, such as studied in relativity, to which affine geometry, affine measurement, is appropriate. Digging into my relativity books would take me too far from other studies in which I’m immersed for a book I’m writing.
I’ll neglect the additional relations and axioms that are progressively added to logical and set-theoretic relations and axioms for analysis of the hierarchy of measurements from ordinal to ratio, but here are examples for the salient types of measurement we actually go about. I take these from Patrick Suppes’ Representation and Invariance of Scientific Structures (2002, 118), without further comment, although with hyperlinks to my pertinent previous expositions. These are one-dimensional scales; a similar story goes for hierarchies of geometry.
Ordinal – Mohs hardness scale; Beaufort wind scale; qualitative preferences.
Hyperordinal – perceived pitch and loudness; utility.
Interval – temperature;* potential energy; cardinal utility.
Ratio – mass, distance, electric current, voltage.