Given the present state of our knowledge, and insufficient thought on my part, my own prescription for the time being is to deal as best we can with … - Arthur R. Jensen

The fact that a reasonable hypothesis has not been rigorously proved does not mean that it should be summarily dismissed. It only means that we need more appropriate research for putting it to the test. I believe such definitive research is entirely possible but has not yet been done. So all we are left with are various lines of evidence, no one of which is definitive alone, but which, viewed all to­gether, make it a not unreasonable hypothesis that genetic factors are strongly implicated in the average Negro-white intelligence difference. The preponderance of the evidence is, in my opinion, less consistent with a strictly environmental hypothesis than with a genetic hypothesis, which, of course, does not exclude the influence of environment or its interaction with genetic factors.

It was little consolation that I had been ‘in good company’ in my ignorance of genetics; in fact, that aspect of the situation seemed even more alarming to me. I was overwhelmed by the realization of the almost Herculean job that would be needed to get the majority of psychologists and educators fully to recognize the importance of genetics for the understanding of variation in psychological traits. Hence, rather than attempting at first to add small increments of original empirical research to the body of knowledge on the genetics of human abilities, I thought my most useful role at that point was a primarily didactic one.

The key theme in Gordon’s chapter, that lends it theoretical coherence, is his clear perception that the guiding force in my own work in mental measurement arises principally from my constant search for construct validity that can embrace the widest range of phenomena in differential psychology. In my philosophy, science is an unrelenting battle against ad hoc explanation. No other field in psychology with which I have been acquainted has been so infested by ad hoc theories as the attempts to explain social class, racial, and ethnic group differences on various tests of mental ability. My pursuit of what I have called the Spearman hypothesis (Jensen, 1985a), which is nicely explicated by Gordon, represents an effort to displace various ad hoc views of the black-white differences on psychometric tests by pointing out the relationship of the differences to the g loadings of tests, thereby bringing the black-white difference into the whole nomothetic network of the g construct. It is within this framework, I believe, that the black-white difference in psychometric tests and all their correlates, will ultimately have to be understood. Understanding the black-white difference is part and parcel of understanding the nature of g itself. My thoughts about researching the nature of g have been expounded in a recent book chapter (Jensen, 1986b). Enough said. Gordon’s chapter speaks for itself, and, with his three commentaries on the chapters by Osterlind, Shepard, and Scheuneman, leaves little else for me to add to this topic.