Can we cleanly define a personality construct? This essay explores how that might not be possible, and why.

Multiple determination

Lou Gehrig’s disease (which afflicted Stephen Hawking and was the subject of the ALS “ice bucket challenge”) is a disease of the motor neurons that control voluntary movement, resulting in total body paralysis, eventually affecting the facial and respiratory systems. The cause in unknown in most cases, and there is no cure. Part of the reason for this is that there is no one way in which ALS develops. ‘Degeneration of motor neurons’ is something we can understand at the relatively macroscopic level of cells and circuits, however there are innumerable ways in which genetic mutations or other afflictions can result in this degeneration. We simply don’t have a handle on the hundreds or thousands of cell processes that can go wrong. In addition, a single malfunction might not be enough to cause a case of ALS; it might take a dozen errors operating in concert.

There is no one-to-one correspondence between a biological process and the symptoms of Lou Gehrig’s disease. A similar problem is encountered in the field of psychiatry. For the last few decades, biologists have tried to track down the genes responsible for disorders such as schizophrenia (operating under the hypothesis that these disorders are fundamentally biochemical). However, what they have found is a massive number of genes linking to schizophrenia at a statistically significant level, but each contributing only a fraction of a percent towards the likelihood of psychosis. The resulting hypothesis is that schizophrenia is a polygenic disorder. Like ALS (and a host of other conditions), it takes many processes acting in concert to result in the disease.

(It might be noted that some social factors have been found to be far more predictive of schizophrenia than genetic factors—but that is a different discussion.)

Many processes, one result. How does this come about? Part of it, I think, is a trick of language. We group individual cases of ALS or schizophrenia as the same disorder, even though the biological factors at play may be totally different. Furthermore, the actual symptoms of the disorder may be mutually exclusive between two individuals (for example, a schizophrenic suffering primarily from flat affect, versus one suffering from hallucinations). Are these really the same disorder? By what criteria are we grouping them? One answer was provided by Ludwig Wittgenstein, who recognized that our cognitive-linguistic categories are not defined by a set of essential features, but by overlapping similarities. Perhaps there is no essential core of schizophrenia! With its many determinants and many manifestations, there could be many schizophrenias, which are nonetheless grouped under the same header. Our language does not represent an exact reality but an approximate one.

Personality

Whether you prefer to use the MBTI, the Big 5, or any number of other measures, the ideas of multiple determination and family resemblance categorization is readily applicable. Investigations of what these constructs are is a favourite pastime of mine and, I assume, of most of my readers. However, these often result in headaches and inter-theory conflict. Which ones are correct? What do we do about those that seem incompatible? I will focus on introversion and extraversion as an example. Here are a few of my favourite theories:

The 20th century psychologist Hans Eysenck saw introversion/extraversion as a measure of how outgoing and interactive a person is with others. He hypothesized that this difference was grounded in a difference in brain arousal. The correspondence is a bit counter-intuitive. An extravert would be characterised by a lower baseline level of cortical arousal, and as a result would seek stimulation to bring their level up to a desired amount. An introvert would be chronically over-aroused, and as a result would seek to minimize the external stimulation they encounter.

Elain Aaron pioneered a new personality category, called the “Highly Sensitive Person”. While technically separate from introversion, there is a high degree of overlap and analogy. Somewhat like Eysenck’s theory, HSPs are characterized by a heightened sensitivity to sensory stimuli, or their own cognition or emotions (or a combination of these). This results in a timid and careful approach to the outside world, as they are more likely to be overwhelmed by a too-intense stimulus.

The biological theory forwarded by many modern psychologists has to do with the dopamine reward system of the brain. Extraverts have been found to be more sensitive to activity in this circuit. In other words, they are more reward-motivated. This has the effect of pulling them more readily and eagerly into active engagement in the outside world. Specifically, this would correspond to the sub-trait of “Enthusiasm”.

Finally, Jung thought of introversion as an attitude that favoured the inner world of the psyche, while extraversion favoured the outer world of things. However, his exploration of the types involves a lot more nuance than this general formulation suggests. Psychological Types is packed with statements and observations that often seem only tenuously related to the central theme. However, this is in keeping with the thesis of my essay. What if there is no one introversion and no one extraversion? What if the only thing binding the many versions together is our categorical mode of thought, rather than any single biological reality?

This is perhaps a bit too strong. For example, it’s an empirical fact that the many facets of the Big 5’s extraversion are highly correlated. There must be some set of biological trends that support this. However, it’s also true that the same individual may be astronomically high in one facet and at the bottom of another for the same over-arching trait. We might conclude that there are some diffuse biological patterns out there, but they are clothed and warped by our cognitive-linguistic constructions.

What’s the take-away here? One may be a more relaxed attitude towards any attempts to find the essence of a psychological category. It may not exist, although a diffuse “family resemblance” pattern might. That is not to say that we shouldn’t scientifically validate our hypotheses about what this pattern is made up of–just that multiple versions might exist in parallel, and that a greater precision is possible when describing two people as introverts, or when observing two cases of schizophrenia. The structure of personality is perhaps less like a series of well-defined islands and more like an ocean: A macroscopic pattern of currents that, when observed more closely, are a heterogenous assemblage of fish and flotsam.

Some links:

ALS fact sheet https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Amyotrophic-Lateral-Sclerosis-ALS-Fact-Sheet

Genetics of schizophrenia https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5380793/

Family resemblance categories https://en.wikipedia.org/wiki/Family_resemblance

Introversion and extraversion https://en.wikipedia.org/wiki/Extraversion_and_introversion

“Highly sensitive person” https://en.wikipedia.org/wiki/Sensory_processing_sensitivity