Thus far, most of this book has been a contribution to the science of individual differences in intelligence. Previously, I have contributed to the science of how cognitive abilities alter over time. I will now venture into the theory of intelligence, partially for its own sake and partially to put my contributions into context.

I want to show that every science needs something I call a meta-theory just as much as it needs fertile scientific theories and, indeed, that there is a relationship between the two. The latter explain and predict phenomena, whether they pertain to the motions of the planets or to intelligent human behavior. The former consists of one or more heuristics – which is to say, concepts that offer advice to theory builders. This advice can be good or bad in the sense that it can set strictures on scientific theories that limit their explanatory potential. The quality of the meta-theory should be measured in terms of the quality of the scientific theories it engenders. In addition, there must be a body of data that allows both verification and falsification. This last is not passive. Some times new data emerge that signal either a flaw in an existing theory and, therefore, the need for a new theory, or the need for a new meta-theory because it appears that current heuristics are giving bad advice about theory building.

I will begin by demonstrating the need for meta-theory even in the most rigorous of the sciences: astronomy, as inclusive of physics and cosmology. When we review the history of astronomy, we will find that the failure to realize that every science has a meta-theory encourages three kinds of error:

1. (1) There is a failure to face the fact that new evidence shows that a hitherto successful theory needs to be revised (type-one error). Often this occurs simply because scientists, like anyone else, are reluctant to embrace new ideas. But sometimes, it is because you are under the spell of a heuristic that makes new theories seem “impossible.”