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I need to ensure the question to which I am giving my response is the same as the question that another party might be asking. It is easy to take for granted that both the former and the latter are always equivalent. They are not always the same, given the different lenses through which people view the world, and I opine that this constitutes the basis for countless misunderstandings that have occurred since time immemorial. It is probably impossible to absolutely reconcile the subjective differences in our understanding of the question, but we can do what we can by clarifying the keywords.

The thing that we need to define here is what is meant by ‘intelligence’. Intelligence is an interesting concept, to me at least, and this concept is certainly rather controversial. In relatively recent times, psychologists seem to have discovered new types of intelligence. This is not unreasonable, particularly if one imagines intelligence as a thing which helps one “move forward successfully” in the world. There are definitely phenomena that would reasonably fulfil such a description. The next few paragraphs outline some “forms of intelligence” that some psychologists have proposed to account for this.

One prominent psychologist who is a proponent of different kinds of intelligence is Robert Sternberg, who is known for his triarchic model of intelligence. As the term ‘triarchic’ suggests, Sternberg’s theory posits that there are three types of intelligence:

1) analytical intelligence (being able to complete academic-style and typical questions that one might encounter on IQ tests; it is often the case that these tasks are fairly well-defined problems with a single correct answer);

2) synthetic/creative intelligence (being able to deal with novel problems by relying on one’s existing set of skills; this may manifest in an individual giving a ‘wrong’ answer because he sees things through a different lens);

3) practical intelligence (“street-smarts”; the way I interpret this is that this is a bit similar to synthetic intelligence, but as the term ‘practical’ suggests, this proposed kind of intelligence pertains to everyday life instead of novel problems; the similarity manifests as requiring the individual to draw on an existing set of skills).

Another prominent psychologist who is perhaps even more well-known as a proponent of different kinds of intelligence is none other than Howard Gardner, who devised his theory of multiple intelligences. This theory of multiple intelligences had a dramatic effect on educational psychology when it was first proposed.

Unfortunately, this supposed dramatic effect does not actually tell us much because educational psychology, among all fields, is arguably the most susceptible to fads. We have heard about the different learning styles, etc. The incorporation of these trends, one after another, may not necessarily be a good thing at all. Gardner’s theory, which was outlined in his 1983 book Frames of Mind: The Theory of Multiple Intelligences, categorically states that there are eight different types of intelligence [1]:

1. Musical-rhythmic
2. Visual-spatial
3. Verbal-linguistic
4. Logical-mathematical
5. Bodily-kinesthetic
6. Interpersonal
7. Intrapersonal
8. Naturalistic

As we have seen earlier, Sternberg proposed the idea of a practical intelligence. We also know how people promulgate the idea of EQ, which is supposedly a measure of the extent of emotional intelligence. From my experience in the equatorial city-state, some people, when referring to a highly sociable person, make statements such as “Waah, look at him sia, he really high EQ leh; vely good people skills sia”, or “Aiya, your studies not so good one, never mind lah, with your high EQ, people will like you at work no matter wat”. There exists a view that such arbitrary categorization of intelligence is absolutely meaningless, and constitutes an entire pile of garbage, and such a view is underpinned by philosophical and technical justification.

Firstly, one cannot just frivolously introduce any old random adjective to qualify a noun. The whole point of having a word is so that it establishes a boundary between what the word describes, and what the word does not describe.

Ok, let me walk you through this. Suppose we can make the word ‘intelligence’ mean whatever we want initially, which does not actually sound entirely unreasonable. The meaning of words at a given moment, after all, depends on what the majority of people at that particular moment who use the word refer to. Such is the dichotomy of descriptivism and prescriptivism in linguistics. For example, the word ‘meme’ is hardly even new at all. It actually has more than one meaning (most people are probably only aware of the one meaning) and has been in use for a long time. Apart from the common meaning which has dominated popular culture for the last decade or so, the word ‘meme’ can also refer to ‘an element of a culture or system of behaviour passed from one individual to another by imitation or other non-genetic means’ [2]. The word ‘meme’, as such, can also be used as a technical word in anthropology, as we can see from this alternate definition.

Anyway, let us consider the issue of ‘intelligence’. Hypothetically, let us suppose that the ability to cook very well is a form of intelligence. It then follows that one may designate another form of intelligence “cooking intelligence”. Unfortunately, the problem with this construct is that the word ‘intelligence’ is now so blasphemed that one cannot even tell what ‘intelligence’ means anymore. So, why is such use of adjectives to qualify intelligence even necessary? Some would argue that such categorization is not necessary at all. English, as it is in 2020, is an extremely rich language, and we have precisely a word to designate what is meant by the ability to cook very well:

Talent (side note: and just like ‘meme’, even ‘talent’ technically has more than one meaning).

We have two separate words: ‘intelligence’ and ‘talent’. The question that the skeptic would then pose is, “How do you determine the difference between intelligence and talent?” That is certainly a valid question because these two concepts are certainly similar to a certain extent. This is where the process of construct validity shines [3].

To illustrate what I mean: suppose we randomly select 1,000 people in Singapore, Australia, or anywhere in the world, and can somehow objectively rank the 1,000 people on their cooking ability. In addition to this, you can rank this same group of people on their ability to multiply two two-digit numbers mentally quickly (e.g. 67 x 54). If these two abilities were intelligences, then the people who could cook well would also be able to multiply two two-digit numbers more quickly mentally on average. If intelligence were the right term to encompass both these abilities, we would be seeing a relatively high correlation between cooking ability and the multiplication ability. However, the actual correlation between the two abilities simply does not meet this criterion (i.e. there is no relatively strong positive correlation).

For intelligence to mean intelligence, every manifestation or form of intelligence that is subsumed by intelligence (i.e. intelligence qualified by whatever adjective you want to slap on it) needs to demonstrate a relatively high degree of correlation with another form of intelligence. Otherwise, they are not the same thing, or at least similar, statistically speaking!

Now, maybe you see where I am going with this.

In order to investigate intelligence (i.e. What is intelligence?), there are perhaps two sub-questions to contend with:

1) If and how does intelligence manifest in the world in which we live?
2) What do we mean by intelligence?

So there is quite clearly an empirical and a definitional issue to be worked out here. People have been studying IQ and intelligence since at least the 1920s. IQ, is a rather unique construct. This is because IQ is the most rigorous concept to have ever arisen from the social sciences. If you think IQ is a load of garbage, you might as well as toss out the field of psychology. This is because the psychologists who first developed intelligence testing were the ones who established the statistical techniques that all subsequent psychologists used to test their hypotheses. IQ is the most stringently and accurately defined construct in psychology. Do you remember the concept of practical intelligence as proposed by Sternberg? Well, according to Professor Jordan Peterson, interest in “practical intelligence” has fallen dramatically since the 90s because when “practical intelligence” is matched head-to-head with standard IQ intelligence, IQ convincingly accounts for the variability in terms of the explanatory power for various phenomena which are associated with success in a particular domain.

IQ is the single best predictor of a person’s success in life. The second-best predictor is the trait conscientiousness, one of the Big Five traits. This could be because unlike IQ, we have not developed a very valid way to measure conscientiousness. Conscientiousness is currently measured by self-report (or even peer reports) on personality tests, which can be easily manipulated to yield extremes because it is so easy to predict what response will yield a higher conscientiousness score. On the other hand, it is statistically impossible for one to be able to just churn out correct answers on an IQ test at a proportion which is beyond one’s threshold of intelligence.

Regarding prediction of life success, conscientiousness yields about r = 0.4 (which is considered a high-end estimate for conscientiousness), whereas IQ yields about r = 0.5 to 0.6. Both correspond to a variance (need to square the r value) of about 16% and 25% (if we are using the low end of r = 0.5 for IQ). So, even low-end estimates of the predictability of IQ of long-term success are superior to what we currently know of conscientiousness by a factor of 25/16 = 1.5 truncated (i.e. IQ has about 1.5 times the predictive power of long-term life success than the second-best predictor we have: conscientiousness, even by conservative standards). Now you can see why intelligent people who are also highly conscientious are so potent in their ability to just destroy the competition. I think this is somewhat rare though (not only because the extremes of traits are rare), because intelligent people may become complacent and essentially choose to be unconscientious, thinking that their intelligence alone is enough to carry them through life. On the other hand, less intelligent people try to be more conscientious to compensate for their lack of intelligence. This concept is concisely expressed in the Chinese idiom:

勤能补拙, which literally means that diligence can mend one’s stupidity. How candid.

Now that we have talked about IQ, let us consider the “different forms” of intelligence again. What does it mean to have different form of intelligence? Suppose we have Form A and Form B, how highly correlated do these forms of intelligence have to be before we can say that they are the same thing? In other words, how uncorrelated do two different forms need to be before they are deemed to be essentially different? The answer to these questions lie in the practical utility of these different forms of intelligence.

Imagine that I am trying to figure out how well Sally will do in university. I measure some metric “a”, which is correlated at r = 0.7 with “b”. These two forms are pretty well-correlated. So, is there any point in measuring both things? The way to figure this out is by doing a statistical analysis: use some sort of dependent variable or target (e.g. Sally’s university GPA), and establish a regression equation. We then need to ask ourselves: can we predict Sally’s GPA better if we use one variable, or two variables? In addition to using different variables in a regression equation, the weights given to the different variables can also be different, and this is reflected by the different coefficients of each variable (e.g. GPA = 2.4a + 1.3b).

So, back to the original question: are there multiple types of intelligence? The first thing we need to ask is “what do we mean by ‘are there’”? The answer to that would be to specify the question.

Step 1: We can try to predict people’s performance in university (as a proxy for long-term success in life), as we have done with Sally. To start, we need to assume that “if intelligence is not associated with university success, then you are probably not talking about intelligence”. In other words, is it reasonable to assume that intelligence and university success share something in common? This is a definitional issue that needs to be settled. Most people would respond affirmatively, although you could technically choose not to (e.g. adopting the view that intelligence plays absolutely no role in university success; rather, other factors such as socioeconomic status, wealth; and of course, these other factors do indeed influence success, which is why IQ and personality traits cannot fully explain the variance in success).

Step 2: So, once we have established this basic proposition, the next thing that we do is to consider each of the supposed different types of intelligence that were outlined above. A measure needs to be made for each of these different types, and the measure needs to be able to measure the same thing (of course within the limits of acceptable experimental error) across multiple instances in the same person. This is absolutely critical because what use is a ruler if it can stretch and change in length (i.e. the actual distance between the marked intervals fluctuate)? The same thing needs to be measured multiple times, and yield a reliable and accurate result, ideally speaking.

Step 3: The next step is to determine the extent of correlation between all these “different types of intelligence”. If we determine that two types of intelligence have basically perfect correlation, then those two types are one or the same type of intelligence. A factor analysis can be done to determine the thing that is common between all the different types of intelligence, which is unsurprisingly: intelligence. It is important to note that this is a proposition, not a fact. If someone were more likely to be musically inclined if he were also inclined in mathematical ability, then the hypothesis would be that there is a single factor that is responsible for all the different manifestations of intelligence.

Step 4: You can also do the same thing not just with Sally’s university GPA as the dependent variable, but also with her PSLE results (end-of-elementary school barrier exam in Singapore), her GCE O-level results, her GCE A-level results, her job performance, and other proxies of success as the dependent variable. Then, what you can say is that the thing that is common between all those supposedly different types of intelligence which predicts Sally’s success across her entire life is called intelligence. THAT common thing, my friends, is how you end up with IQ.

In other words, IQ, which measures g (that you can see in that huge circle at the top of the above diagram), is what is common among all possible intelligence tests. Of course, people are going to debate this because “what constitutes a test?” Psychometricians have managed this by essentially saying that not everything that is measured is called intelligence.

For example, extraverted people are more socially adept. Are we going to call that intelligence? Of course not! We going to call that personality, specifically extraversion.

Are people who can tolerate more stress deemed more intelligent? No! That is yet another component of personality: low neuroticism.

Are people who are more co-operative more “emotionally intelligent”? No again! Are people who are more competitive less intelligent? As such, this is also yet again another component of personality: agreeableness/disagreeableness. Females are more agreeable than males, and this certainly contributes to the manifestation of how many managerial, leadership roles, and what society deems as “positions of authority and power” are predominantly occupied by men.

The final question then is, once IQ and personality traits have been factored in, are there any differences between the “different types of intelligence”?

Once IQ and personality traits have been considered, there are NO differences between the so-called different types of intelligence.

I think the only thing responsible for the actual variation in the manifestation of “different types of intelligence” that we observe over time in a particular person is domain-specific deliberate practice (e.g. engaging in more deliberate practice on the piano would yield better performance ceteris paribus), which of course cannot be due to inherent intelligence as we have already controlled for IQ.

The reason that many people are proponents for “different types of intelligence” lies in the fact that people are uncomfortable with the fact that there are real tangible differences between individuals. The idea that someone is naturally predisposed to be able to solve problems cross-domain and across time better than another person is frightening to some. Moreover, I suspect that many are uncomfortable discussing intelligence because an individual’s intelligence has been erroneously conflated with his intrinsic worth as a human being. Intelligence is an issue which warrants more discussion in society but the reality is that many people in the world are insufficiently mature to discuss the implications of our current understanding of intelligence on social and educational policy.

NL
2 June 2020

References:
Peterson, JB (2016). “2016 Personality Lecture 13: Openness and Intelligence”. Date published: 30 March 2016. Date accessed: 2 June 2020. https://www.youtube.com/watch?v=qRFxulvRC7I
Peterson, JB (2017). “2017 Personality 18: Biology & Traits: Openness/Intelligence/Creativity I”. Date Published: 19 April 2017. Date accessed: 2 June 2020. https://www.youtube.com/watch?v=D7Kn5p7TP_Y

[1] Slavin, Robert (2009), Educational Psychology, p. 117, ISBN 0-205-59200-7
[2] Google Dictionary (2020). Meaning of ‘meme’. Accessed online: 2 June 2020.
[3] Trochim, W (2020). Construct Validity. Accessed online: 2 June 2020.
https://conjointly.com/kb/construct-validity/