Measurement is a fundamental part of human life. It is used in a wide variety of activities, from determining the temperature of water to judging the suitability of a job candidate. It is also important for the development of healthcare, particularly in assessing the need for treatment and measuring the effects of care. Yet, despite its central role in our lives, the concept of measurement has been the subject of intense philosophical debate. This article surveys the main viewpoints and explores some of the central issues in this area.
Mathematical theories of measurement concern the conditions under which relations exhibited by numbers (equal, sum, difference and ratio) can be used to express relationships among objects. They are not, however, necessarily related to the properties exhibited by the objects to which they are applied. For example, the relations exhibited by the number 60 do not correspond to the relation between the temperatures of two different objects, since there is no such thing as a zero point in the Celsius scale.
Realists – such as Brent Mundy and Chris Swoyer – take an empirically-reflective measurement in life view of measurement, arguing that the axiomatic treatment of measurement scales in mathematical theories of measurement is misguided. Instead, they argue that a proper interpretation of the axioms reveals that they refer to universal magnitudes rather than to observable properties or relations (e.g., 5 meters long). They thus argue that the measurement process consists of discovering and approximating such mind-independent numbers.
In a more abstract vein, information-theoretic accounts of measurement are based on an analogy with communication systems. An object’s state is encoded into an internal signal, sent to an external measurement instrument and decoded into a reading (output). The accuracy of this transmission depends on features of the system as well as on the level of noise in its environment.
The resulting theory-laden account of measurement emphasizes that the knowledge resulting from measurement consists not of observations about particular objects, but rather of the a priori properties and relations instantiated by those objects. This shift in emphasis helps to highlight the fact that measurable quantities are always theory-laden.
Despite the wide range of philosophical viewpoints on the nature of measurement and its relationship to our concepts of measurable quantity, most of these perspectives share certain common features. This is especially the case with respect to the metaphysics, epistemology and semantics of measurement, which are all intertwined. Consequently, this entry will avoid elaborating on the many discipline-specific issues that have been raised in these areas and will focus instead on presenting some general aspects of the issue. This will allow for a more comprehensive overview of the various viewpoints on measurement than would be possible in a single essay. For those interested in a more detailed discussion of the issues involved, references to relevant literature are provided. This is a peer-reviewed version of an article published in the journal Measurement and Philosophy of Science, Volume 2, Issue 1. Copyright 2014 Springer-Verlag.