Defining Intelligence: “It’s a trap!”

It is a favourite debating ploy in discussions about human intelligence to ask for a definition of the construct. One meaning of ‘define’ in the Oxford English Dictionary is ‘give the exact meaning of’. If differential psychologists are daft enough to attempt this, they will find they have been tricked into delivering a hostage to fortune, the premature issue will be rent by inquisitors. (p. 1)

Deary, I.J. (2000). Looking down on human intelligence: From psychometrics to the brain. Oxford University Press.

Deary advises intelligence researchers to instead try to mark the boundaries of the concept of intelligence. Some scholars in other disciplines also have ambivalent relationships with exact definitions. Mike Brown, who discovered several “dwarf planets” and many other large objects in our solar system beyond Pluto, explained why he does not take seriously the International Astronomical Union’s official definition of the term planet that excluded Pluto:

In the entire field of astronomy, there is no word other than planet that has a precise, lawyerly definition, in which certain criteria are specifically enumerated. Why does planet have such a definition but star, galaxy, and giant molecular cloud do not? Because in astronomy, as in most sciences, scientists work by concepts rather than by definitions. The concept of a star is clear; a star is a collection of gas with fusion reactions in the interior giving off energy. A galaxy is a large, bound collection of stars. A giant molecular cloud is a giant cloud of molecules. The concept of a planet—in the eight-planet solar system—is equally simple to state. A planet is a one of a small number of bodies that dominate a planetary system. That is a concept, not a definition. How would you write that down in a precise definition?
I wouldn’t. Once you write down a definition with lawyerly precision, you get the lawyers involved in deciding whether or not your objects are planets. Astronomers work in concepts. We rarely call in the attorneys for adjudication. (p. 242)

Brown, M. (2012). How I killed Pluto and why it had it coming. Spiegel & Grau.