Prestigious Black national merit finalist GondwanaMan writes in the comment section:

… I’ve heard Thomas speak multiple times over the past 10 years and he seems very intelligent but I’ve heard mixed things about his behavior/intellect. Maybe PP can do an IQ analysis I would be very interested…

Thomas came from nothing to become one of the most powerful men on the planent. He is clearly intelligent compared to the average American, but in my opinion he would score lower on an IQ test than most other members of the super-elite.

For one thing, Thomas is known for his chilling silence. Unlike other supreme court judges who ask questions and make comments, Thomas has been largely silent for decades, much like the dim-witted Jason from the Friday the 13th movies.

Conservatives tend to score lower on IQ tests than liberals and blacks tend to score lower than whites, but because blacks are almost never conservative, the rare combination of being both conservative and black doesn’t bode well.

Of course conservatism is a vaguely defined moving target so Thomas may have very intelligent reasons for his political views that are actually quite liberal in the true spirit of the term. For example Thomas opposes affirmative action, not because he’s anti-black, but because he saw first hand how being seen as a token devalued his Yale Law degree. While white law grads had elite law firms at their beck and call, Thomas had to apply to dozens of firms to even be considered. Of course this was the 1970s when there was a lot more racism.

In general he felt that affirmative action benefits light-skinned blacks from elite backgrounds while dark skinned blacks like himself had to work much harder. Of course if racial IQ differences are genomic, we’d expect darker skinned blacks like Thomas to have lower IQs (on average) than their lighter skinned peers like Obama and Corey Booker. From page 45 of the book Strange Justice written by Jane Mayer and Jill Abramson:

Not only was he short, and in his teen years slight, but he also had exceptionally African features years before the Black is Beautiful movement made them desirable. “He was darker than most kids, and in that generation, people were cruel,” recalled Sara Wright, a librarian for the Savannah Morning News who attended elementary and junior high school with Thomas. “He was teased a lot and they’d call him [N word redacted by PP, 2020-03-02] Naps” for his tightly curled hair. “A lot of the girls wouldn’t want to go out with him.”

Thomas himself remembered being called “ABC,” or “America’s Blackest Child.” Even friends recollect taunting him that “if he were any blacker, he’d be blue.” As Lester Johnson, who is now a lawyer in Savannah, recalled, “Clarence had big lips, nappy hair and he was almost literally black. Those folks were at the bottom of the pole. You just didn’t want to hang with those kids.

…The most prominent families in town since before the Civil War were for the most part what a local history of African-Americans called “high yellow,” or mulatto. At the same time, many of those with pure African bloodlines, like Thomas were made to feel inferior.”

…At Yale he talked bitterly about the “light-skinned elite” blacks who had it easier than the darker ones.

pg 45 of Strange Justice

Of course race is only one variable that correlates with IQ and we shouldn’t give it too much emphasis, as some very dark skinned blacks score far higher on IQ tests than 99% of whites and East Asians, however as the below photo with George H.W. Bush shows, Thomas has many physical traits that put him at risk for low IQ.

Thomas is much shorter and more muscular than his fellow elite George H.W. Bush. Height is positively correlated with IQ and weight/height ratio is negatively correlated with IQ. Also the cranial capacity of the elder Bush seems to dwarf Thomas’s. But to his credit, Thomas is wearing glasses and myopia is thought to be genomically linked to high IQ.

So what is his IQ?

It’s unclear if Thomas ever took an official IQ test but he almost certainly took proxy versions like the SAT and LSAT. However these scores are not known so we’re left only with his grades.

The book Strange Justice describes his academic behavior at Holy Cross college:

But much of his time was spent alone, usually studying. His classmates recalled that when they went to dances at nearby schools on Saturday nights, Thomas often preferred to stay in the basement of the college library. When the school threatened to shorten the Saturday night library hours, he petitioned the authorities to keep the facility open. And when others went away during holidays, he stayed in the otherwise empty school, explaining later that he viewed such breaks as a valuable opportunity to get ahead of the other students.

Academically, his efforts paid off. He wrote to a friend that he had managed to maintain a 3.7 grade point average, and he graduated in 1971 with honors, ranking ninth in his class

According to The New York Times, Thomas’s grades at Holy Cross were in the top 7% of his class.

Let’s assume grades are simply an average of IQ and hard work (averaging is appropriate because two variables are not correlated). If we assume Thomas was in the top 1% in hard work (skipping holidays, petitioning the library to stay open), which is 2.33 standard deviations above the class average, how high would his IQ have to be to end up in the top 7% (+1.6 SD). Simple algebra tells us that if he was +2.33 SD in hard work (relative to Holy Cross students), his IQ could be no higher than +0.87 SD for his grades to be +1.6 SD.

So now that we estimate Thomas’s IQ was +0.87 SD relative to Holy Cross students, we need to know what their IQ distribution was.

Circa 2014 Holy Cross had a median SAT score of 1280 out of 1600 which equates to a mean IQ of 128 (U.S. norms).

However we know Harvard students went from an SAT IQ of 143 to an IQ around 128 with an SD of 12 on a test not used to select them (one third regression to the mean) so the actual IQ distribution at Holy Cross (in 2014 and perhaps historically) was likely around 118 with a standard deviation around 12 (compared to the U.S. distribution of 100 with an SD of 15).

Thus Thomas’s estimated IQ is 118 + 0.87(12) = 128 (U.S. norms) or 127 (white norms). In other words, smarter than 96% of white America.

Is this estimate too high?

There is reason to think this estimate might err on the high side. For example on page 201 of the book Yale Law School and the Sixties: Revolt and Reverberations it states:

…Associate Dean Ralph Brown recalled that “we were admitting blacks very indulgently, and a lot of them could barely do the work.” When courses required in-class exams, minorities tended to end up “in the bottom,” Charles Reich said. “You couldn’t disguise that”. One could get around it, he added, by having students write papers that, after several drafts, might well deserve a high grade, as he did for Clarence Thomas. But first semester courses required exams.

Since first semester Yale Law courses require exams, perhaps the best estimate of Thomas’s IQ can be found in this paragraph from Strange Justice:

His academic records remain, with his consent, sealed. But professors and administrators from his era recall him as an average student, hard-working but not particularly brilliant. There is only one professor –Thomas I. Emerson– whose records have been made public. Thomas elected to take Emerson’s first-year course on politics and civil rights in 1972, and Emerson’s notes show that he finished the class near the bottom, with a 69 for the semester. One of only two students who scored lower was Thomas’s friend and later witness against Hill, John Doggett.

Interestingly Doggett is also a black conservative.

Assuming about 20 students per class room, being in the bottom three puts Thomas in the bottom 15%, or roughly 1.13 SD below the class mean.

Although students at the best law schools average around IQ 145 on the LSAT, they likely regress to 128 (with an SD of 12) on tests not used to select them. Thus if Thomas’s bottom 15% performance in Emerson’s law class implies an IQ of:

128 – 1.13(12) = 114 (U.S. norms) or 112 (U.S. white norms).

Higher than 79% of white America.

That sounds about right.

[this article was lightly edited on March 3, 2020]