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The invention of the thermometer made it possible to objectify the attribute of temperature, to quantify it, and to measure it with a high degree of reliability. With some important qualifications, the situation is similar in the case of intelligence tests. … To object to this procedure by arguing that the IQ cannot be regarded as being interchangeable with intelligence, or that intelligence cannot really be measured, or that IQ is not the same as intelligence, is to get bogged down in semantic morass. It is equivalent to arguing that a column of mercury in a glass tube cannot be regarded as synonymous with temperature, or that temperature cannot really be measured with a thermometer. – Jensen, 1973: 343, 345; Can we and should we study race differences?

In assessing the methodological role of IQ tests in each of the research programmes, thermometers provide an instructive analogy, for the relationship of thermometers to thermodynamics is rather similar to that of IQ tests to theories of intelligence. (Urbach, 1974: 104)

‘if the measurement of temperature is scientific (and who would doubt that it is?) then so is that of intelligence.’ (Eysenck, quoted in Nash, 1990: 131)

If psychology can’t be measured then that is a huge barrier in the way of psychology actually becoming a science like all of the other sciences it tried to mimic. Psychology has been trying to become a legitimate science for years now. There is of course the so-called replication crisis in psychology (Baker, 2016; Oberauer and Lewandowsky, 2019), but psychologists say that this doesn’t extend to “intelligence”. However, I have argued that psychologists are mistaken. If psychological traits exist (and they do), and if they are a product of immaterial minds (they are), then how could they be measured by empirical methods? That’s the troubling issue for psychology—if psychometrics isn’t measurement (Uher, 2021), and if psychological traits aren’t quantitative (Michell, 1997) and if psychological phenomena aren’t manipulable nor controllable (Trendler, 2009), then how can psychology be an empirical science (Smedslund, 2016)?

Why the Berka-Nash measurement objection matters and what it means for temperature and IQ

This objection is simple—something can be said to be measurable if and only if there is a specified measured object, object of measurement and measurement unit (Berka, 1983; Nash 1990). Where a specified measured object is the thing or phenomenon to be measured, an object of measurement refers to the property that is measured, and the measurement unit refers to a standardized unit which is used to quantify the specified measured object. Since there are, by admission of psychologists, no measurement units in psychology (specifically for IQ, as admitted by Haier (2014, 2018) then it seems that a science of psychology—a science of the mind—is impossible.

In the past, IQ-ists have claimed that their discipline is a science and if temperature can be measured, why can’t intelligence? Nash (1990: 131) puts this succinctly:

First, the idea that the temperature scale is an interval scale is a myth and, second, a scale zero can be established for an intelligence scale by the same method of extrapolation used in defining absolute zero temperature. In this manner Eysenck (p. 16) concludes, ‘if the measurement of temperature is scientific (and who would doubt that it is?) then so is that of intelligence.’ It should hardly be necessary to point out that all of this is special pleading of the most unabashed sort. In order to measure temperature three requirements are necessary: (i) a scale, (ii) some thermometric property of an object and, (iii) fixed points of reference. Zero temperature is defined theoretically and successive interval points are fixed by the physical properties of material objects. As Byerly (p. 379) notes, that ‘the length of a column of mercury is a thermometric property presupposes a lawful relationship between the order of length and the temperature order under certain conditions.’ It is precisely this lawful relationship which does not exist between the normative IQ scale and any property of intelligence.

Basically, what is the property that IQ tests measure? The answer to the question, it seems, is elusive. Contrary to popular belief of IQ-ists, they do not have any refuge by attempting an argument from analogy on IQ tests and thermometers. IQ tests measure intelligence, says the IQ-ist, just like thermometers measure temperature. However, there is no property measured by IQ tests while the property measured by thermometers is thermal expansion—which is a physical property. Thus, contra Eysenck and Jensen, their attempted analogy fails. The construct of temperature was validated in a non-circular manner independent of the original measurement tool used to measure it (see Chang, 2007). The same cannot be same for IQ.

In a wonderful discussion about the measurement of temperature and how it is nothing at all like “intelligence” (and by identity, how the thermometer is nothing like the IQ test), Evans and Waites (1981: 181) write in their book IQ and Mental Testing: An Unnatural Science and its Social History:

The comparison between IQ test development and thermometer development would be appropriate if the history of thermometers had been quite different from what actually took place. Suppose that it was as follows. A crude thermometer was devised. Further thermometers were then invented, and accepted as satisfactory provided that they yielded results which correlated reasonably well with those obtained from the original device. Research into the relationship between heat and other things produced roughly similar results when different thermometers were used, and when this was not the case, a variety of ad hoc explanations were put forward to account for this. It was not considered necessary to investigate the anomalies further because the rough similarities were considered to be much more significant than the anomalies. In this hypothetical case, we have a very good analogy with the development of IQ tests and with research into such topics as the heritability of IQ, and the relationship between IQ and educational achievement. The reason why there is such a sharp contrast between IQ psychology and what actually took place in the theory of heat and thermometer development follows from our discussion of contemporary psychobiology in Chapter 4. It proved extremely productive to conceive of heat as a unidimensional measurable quantity; it is not productive to conceive of human intelligence in this way.

IQ-ists have claimed for decades that IQ (“intelligence”) is basically identical to temperature. Going back to Nash above, there was a scale, a thermometric property of an object, and a fixed point of reference, along with a lawful relationship between the length of mercury in a thermometer and the temperature, say, outside. There is a theory that is used to validate temperature and thermometers and there is no such sinilar theory for IQ and it’s relation to “intelligence”; there is no validating theory for it like there is for temperature.

The kinetic theory of gases validates temperature and thermometers. The length of a column of mercury increases or decreases due to the surrounding temperature of the environment that the thermometer is in. As the mercury in the thermometer is heated (meaning, when the temperature in the environment increases), this results in an increase of the kinetic energy of the mercury particles. So as this kinetic energy increases, the mercury particles move faster and faster while colliding with each other which then causes the mercury in the thermometer to increase. Meanwhile, as the temperature in the environment deceases, the average kinetic energy of the molecules decreases which then causes the mercury to contract and subsequently decrease in the thermometer. This relationship is quite clearly lawlike and a physical relationship.

The arguments

Now here are a few more arguments that psychology can’t be measured.

P1: Scientific measurement requires a consistent and standardized way of observing or quantifying an object or phenomenon.
P2: Psychological traits cannot be observed or quantified in a consistent or standardized way.
C: So psychological traits cannot be measured scientifically.

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P1: If psychological traits are a meaningful object of scientific measurement, then they must be observable or measurable in a consistent and standardized way.
P2: Psychological traits cannot be observed or quantified in a consistent and standardized way.
C: So psychological traits aren’t a meaningful object of scientific investigation.

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P1: If X is a specified measured object, or phenomenon, then X can be measured using a standardized measurement unit.
P2: Psychological traits cannot be measured using a standardized measurement unit.
C: So psychological traits aren’t a specified measured object or phenomenon. 

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P1: If temperature and IQ were similar, then there would be a theory of cognitive processes similar to the kinetic theory of gases.
P2: There is no theory of cognitive processes similar to the kinetic theory of gases.
C: Thus, temperature and IQ are not similar (MT, P1, P2)
P3: There was a theory of temperature developed in the past.
P4: There was no theory of cognitive processes developed in the past.
C2: So temperature and IQ are not similar and there is no theory of cognitive processes similar to the kinetic theory of gases. (MT, C1, P3, P4)

P1 sets up the conditional relationship between IQ and temperature being similar, and a theory of cognitive processes. P2 states that there is no theory of cognitive processes that is akin to the kinetic theory of gases. The conclusion then follows that IQ and temperature are not similar. P3 and P4 are then deployed to show that while there was a theory developed to account for and explain temperature, there was no such theory for human intelligence (“IQ”) , per Ian Deary: “There is no such thing as a theory of human intelligence differences—not in the way that grown-up sciences like physics or chemistry have theories” (quoted in Richardson, 2012).

So it is therefore false, contra the protestations from Jensen, Eysenck, and Urbach, that IQ is similar to temperature, since temperature is a physical property. If you ask any IQ-ist “What property is being measured by IQ tests?”, they won’t be able to provide a satisfactory answer. That’s because there is no theory behind what the tests are “measuring”. Temperature is a fundamental aspect of the physical world. It is a physical property. Since science only deals with physical properties and phenomena, then it can deal with temperature. Since psychological traits are immaterial, they are therefore immeasurable since they lack a specified measured object, object of measurement and measurement unit.

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P1: If temperature and IQ were similar, then they would share similar properties and characteristics.
P2: Temperature is a physical property that can be measured using various devices.
P3: IQ is a psychological construct, and can’t be measured using physical instruments.
C: So temperature and IQ do not share similar properties and characteristics.

P1 is based on the idea that if temperature and IQ were similar as had been asserted for years by hereditarians, then they would have theories explaining then along with the underlying mechanisms for them. This has occurred for temperature, but not for IQ. So the premise suggests that temperature and IQ are not similar. P2 is based on the idea that there is a well-established theory of temperature, but not IQ (see Richardson and Norgate, 2015 for examples of real, valid measures of unseen functions and mechanistic relations between variables). There is no overarching theory of IQ that can explain all aspects of it in the same way that the kinetic theory of gases explains temperature. P3 and P4 are based on historic facts: as alluded to above, the kinetic theory of temperature explains the behavior of molecules which then explains the expansion of mercury in a thermometer (it explains the expansion and contraction of materials and temperature); while there is no single theory that can be considered to be such an explanation for IQ. Therefore, temperature and IQ are not similar, and attempts to treat them as similar are unwarranted.

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Now here is the master argument, which I call the physical properties and theories argument, which establishes that temperature is measurable since it is a physical property with an established theory while the same isn’t true for IQ.

P1: Physical quantities are measurable.
P2: Temperature is a physical quantity.
C: Thus, temperature is measurable. (MP, P1, P2).
P3: Psychometric intelligence (“IQ”) is a hypothetical construct.
P4: Hypothetical constructs are unobservable.
P5: If something is unobservable, then it is immeasurable and so it cannot be quantified.
C2: Psychometric intelligence is unobservable and so it is immeasurable thus it can’t be quantified (MT, P1, P3, P4, P5).
P6: The validity of a measurement is based on a well-established theory.
P7: There is a well-established theory of temperature.
C3: Therefore, measurements of temperature are valid. (MP, P6, P7)
P8: There is no well-established theory of cognitive processes.
P9: Psychometric intelligence is (supposedly) a measure of cognitive processes.
C4: Thus, measurements of psychometric intelligence lack validity. (HS, P6, P7, P8,P9)

Conclusion

As can be seen, even if we accept claims from IQ-ists (and we definitely don’t have to), then what they try to argue for still fails. Over the decades, quite a few authors have attempted an argument by analogy—that if the measurement of temperature was a valid scientific method, then so was the measurement of intelligence using IQ tests. However I have provided a few (more) arguments for the claim that IQ is nothing like temperature since temperature is a physical property and psychological traits (IQ) have no theory so they therefore cannot be measurable (along with numerous other arguments). The fact of the matter is, contra Jensen, Eysenck and Urbach, thermometers and temperature are not related—that is, they are not identical with—IQ tests and IQ/intelligence, since one is physical and based on actual physical measurements with a theory and a specified measured object, object of measurement and measurement unit. The same, obviously, cannot be said for IQ. Thus, the claims put forth by Jensen, Eysenck and Urbach fail. Measurement by fiat—like “intelligence”—aren’t theoretically justified (Berka, 1983: 131). I have, yet again, shown that IQ is not a physical measurement, and so, IQ isn’t a physical property, and that there is no specified measured object, object of measurement and measurement unit for IQ. Therefore, temperature is NOT to IQ like thermometers are NOT to IQ tests.

The scale for temperature measurement was originally defined by stipulation with regard to the mercury thermometer. In this case, the notion of temperature can be interpreted only for materials within the range of their values between the point of thawing and the boiling point of mercury. Since an empirical law exists, according to which one may view temperature (under a constant pressure) in this range as a function of volume, we can measure the temperature of materials indirectly, on the ground of laws, by means of a gas thermometer, i.e., by virtue of establishing the volume which will be occupied by a definite standard amount of gas (under the specified pressure) in contact with the measured material. Should we now use a derived measurement by stipulation, we might decide that temperature will also exist outside the range of the original measurement of the functions of volume. Within the framework of measuring temperature by means of a mercury thermometer, the use of a gas thermometer represents a derived measurement on the basis of laws, while outside this framework it represents a derived measurement by means of stipulation. (Berka, 1983: 130)