I was once sat next to an economist. He asked me what I did for a living and I told him.

“Education is all about signalling,” he explained. It turns out that ‘Signalling Theory’ was his specialist subject.

“Take art history degrees, for example,” He continued, “they are of no real use. What you are really saying by doing an art history degree is that you are smart otherwise you wouldn’t invest so much time and money in completing one. This is then what you are signalling to a future employer.”

I don’t know about art history degrees – maybe he’s onto something there – but as a general theory of education, signalling theory sucks.

This is because intelligence is two things and yet people invariably think of it as just one.

The first component of intelligence is raw processing power. This is how much you can manipulate in your working memory. We might call this ‘fluid intelligence’ and there is not much you can do about it. People have devised ‘brain training’ activities that attempt to improve fluid intelligence through exercise, as if it were a muscle. The evidence suggests that this kind of exercise makes you very good at the training task but that this doesn’t transfer to anything else.

When some people argue that intelligence being hereditary then it might be because of genes that determine fluid intelligence. If that’s the case then what is the point of all of this education? Our intelligence is preordained.

But there is another component to intelligence that we might call ‘crystallised intelligence’. Loosely, this is what you know. If you know your multiplication tables then you might be able to solve multiplication problems more quickly and accurately than someone who has greater fluid intelligence than you but who doesn’t know their tables.

Consider two plumbers. One is a smart trainee and the other is an old hand. Who will solve the plumbing problem first? Well the old hand will have plenty of previous plumbing problems to compare it to, a process that will happen without conscious effort. This is greater crystallised intelligence.

Education is the process of growing the crystallised intelligence of individuals. Unfortunately, we cannot predict the future either in general terms or the future for any particular individual. We do not know what mental resources they might want or need. So we make a best guess. We teach them that which has endured on the plausible assumption that knowledge that has proved useful or fulfilling in the past will do so in the future.

It is possible that crystallised intelligence has a genetic component. People might inherit personality traits that make them more inclined to stay indoors and read books. Yet I think that most of the time the nature versus nurture people are talking past each other.

Those who believe that intelligence is largely genetic conceive of it as the fluid component only and those who want to stress a growth mindset are actually conceiving of intelligence as the crystallised component. This latter group don’t seem to realise this and talk as if they are somehow growing the brain through exercise. They are not.

My economist had made the error of thinking of intelligence as only the fluid component and so had undervalued the role of knowledge. I tried to explain this to him but he seemed to struggle to grasp what I was taking about.

Perhaps he wasn’t very smart.


8 thoughts on “Smart

  1. You would hate futurist economist Robin Hanson’s blog which is all about signalling, cognitive biases etc but a great read. Your caveats aside, signalling theory does have some valuable insights to offer about education. Not in terms of a general theory of education, which to be fair it doesn’t attempt to be, but possibly in terms of explaining relative status amongst higher education institutions, parental rivalry to access those higher status institutions (primary, secondary and tertiary) for their children tendency of employers to hire people from those high status institutions to signal status to clients and many others. Signalling theory probably also has useful insights even if only to argue against)to offer on a wide variety of issues regarding school and even subject choice as well. It’s well worth a look.

  2. Iain Murphy says:

    Thanks for introducing the idea of signal theory, I agree it sounds like his example is poor. Wouldn’t a better example for teaching be that students work alters to reflect the interests of the assessor/teacher something seen all to often in the classroom.

    Like the idea of two types of intelligences and your example. Certainly I want the best solution from a tradesman but it’s worth remembering that crystallised knowledge can also be historically accurate. The plumbing solution is no good if it involves techniques that are now illegal or dangerous. This can be true as well in the classroom when teachers are unwilling to change approach with the changing requirements of teaching (another signal approach?)

    Growth mindset looks more at the fluid intelligence. By your definition “how much you can manipulate in your working memory” will be effected by how willing they are to engage and fail at the task and this is mindset. The ability to enter fixed mindset can be triggered by the crystallised mind suggesting little or no knowledge in this area. Fixed mindset can also occur when there is to much crystallised thinking and not enough fluid thinking as pride in knowing more stops that thinking from being evaluated and changed.

    How do you feel explicit vs constructive teaching engages the two thinking types?

    • I’m not sure about your third paragraph. The evidence suggests that fluid intelligence can’t really be enhanced and so, if mindset interventions work, it is doubtful that they work in this way. I am also not sure what you mean by the ‘crystallised mind’ and ‘too much crystallised thinking’. Perhaps the terms ‘fluid’ and ‘crystallised’ are causing some confusion here. The Wikipedia page on this subject does suggest that this may happen.

      • I think there is some confusion here between what signalling theory can perhaps explain and what it can’t. You reject signalling as having explanatory power for explaining education because you feel that “Education is the process of growing the crystallised intelligence of individuals.” I imagine signalling theory fans would probably reject this definition immediately (as with your economist) by taking some sort of line such as education is the process of signalling status to potential mates, employers, friends, rivals etc. If we are going to reject the signalling view on education and replace it with your view then we turn would need to be able to use your view to explain at least some of the following that signalling theory can provide insights on:
        1. Relative prestige of individual subjects versus each other
        2. Why parents who are against private schooling on elitist grounds are happy to spend more on a house in the right area for entry to prestigious state schools
        3. Why there is lower interest in learning itself versus gaining qualifications.
        4. Why there is parental pressure for students to form friendships with higher status families/peers etc
        5. Why people ‘massage’ their educational qualifications on job applications
        and so on, in fact if education’s purpose was to grow the crystallised intelligence of individuals and not to signal to potential employers then wouldn’t this be counterproductive?

        I am also somewhat unconvinced that this statement supports your point “We do not know what mental resources they might want or need. So we make a best guess. We teach them that which has endured on the plausible assumption that knowledge that has proved useful or fulfilling in the past will do so in the future.” Because we don’t really do this, in fact there are different sets of what is past knowledge is in different types of schools. Eg: Higher status/elite schools (in social terms) will offer classics etc. Signalling theory may offer some useful insights as to why this might be.

        Thanks for a very interesting post,

      • If signalling theory fans reject this definition then they might be making a mistake. I am sure that education can be used in many of the ways that you describe above. But that doesn’t mean that this is what education *is*. It’s a bit like claiming that a race-horse is a means for signalling the wealth and status of it’s owner and not a fast-running, four-legged mammal. This would clearly be a little absurd. I sometimes think economists have a tendency to run away with their theories.

        Interestingly, much of the debate between educators at the moment is about why different schools teach different content. I believe that this is due to flawed ideas about education and its aims. I am not sure why a school would choose a curriculum that signalled that it was lower status by selecting content that was not associated with the elite.

      • Iain Murphy says:

        Hi Greg

        The article you link too suggests that testing of the two intelligences can assess the effectiveness of one or the other so clearly when engaging that pat of the brain you are thinking with that form of intelligence, hence crystallised thinking involves crystallised intelligence in the crystallised brain or mind.

        I think it is dangerous to suggest that one intelligence can’t be developed. Crystallised intelligence happens to be easier to develop, just introduce facts and information. The fluid intelligence is harder but far more important now that information is readily available. No longer do children need to be brought to a teacher or library to discover knowledge, too many facts are simply google able (not saying that is good, just a reality). So it becomes the synthesis of ideas, deciding whether the facts are good or biased that becomes important and this is fluid intelligence or falls outside the scope of this model. This can and should be trained as with careful direction allows for better recognition of crystallised intelligence knowledge.

  3. Stan says:

    Greg and Iain,
    I think it is dangerous to suggest that people cannot fly without mechanical aid. A quick search of google shows there is a vigorous debate on this subject. A growing number of people believe it will solve a number of modern day problems: reducing energy consumption, obesity, traffic congestion and at the same time as enabling a reasonable approximation of the game Quidditch.

    While there are naysayers these people are focused too much on the physical impossibility and not the numerous benefits.


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