Immanuel Kant's IQ: What Catharine Cox Actually Found

The rating: 135, then 145

Kant is in the book. Catharine Cox's The Early Mental Traits of Three Hundred Geniuses (Stanford University Press, 1926) gives him a full case study among those "rated at AI IQ 130 to 140." Her raters read the biographical record and assigned two figures: an AI IQ of 135 for development to age 17, and an AII IQ of 145 for ages 17 to 26. Cox graded the reliability of the data behind both at .43, below the median for her sample. Our Immanuel Kant profile covers the life beyond the numbers.

The inputs were concrete. His father was a harness maker in Königsberg. His mother taught him about plants and the night sky before he started school. At eight and a half he entered a pietist school, the Collegium Fridericianum, and from 9 to 14 he held first place in his class. He entered the University of Königsberg in 1740, at 16, and published his first book, Thoughts on the True Estimation of Living Forces, in his mid-twenties. Cox added a telling line: "apparently no one of his schoolmates or teachers suspected Kant's genius."

On the modern scale, 135 is roughly the top 1 percent and 145 about three standard deviations above the mean. Cox, however, framed her ratings on the older Stanford-Binet, and the method behind all such figures is explained in our guide to historical IQ estimates.

Cox doubted her own 135

The most important sentence about Kant's IQ is in Cox's discussion of the 135 group. She wrote that "in several of the cases the rating of 135 clearly involves a regression for lack of data." Then she named names: the group's "true upper limit, set by such youths as Cousin, Darwin, Erasmus, Da Vinci, and Kant, is probably in the IQ range above 160."

In plain terms, Cox believed Kant's rating was dragged down by thin records, not by a modest mind. Her method rewarded documented precocity: a child whose tutor recorded Latin at five would score higher than a child whose schooling left few notes. Kant's greatness arrived late and on the page, not early and in family letters.

Where the 175 comes from

The number that turns up for Kant on list sites is 175. It is not a test score and not Cox's rating. It comes from her attempt to correct for incomplete records, which she knew pushed every estimate toward the average. Cox called the correction "a crude approximation," one that indicated "a point below which the true IQ probably did not fall." Secondary tables that reproduce her corrected figures list Kant at about 175.

Read that way, 175 is a statistically adjusted floor from the 1920s, built on data Cox graded at .43. It is defensible to cite with that label. It is misleading to cite as "Kant's IQ." The raw ratings, 135 and 145, are the figures her case study actually prints.

The evidence of the mind

Kant's record is one of late, overwhelming output. In 1755 his Universal Natural History and Theory of the Heavens proposed that the solar system formed from a rotating cloud of matter, the nebular hypothesis. In 1770 he became full professor of logic and metaphysics at Königsberg. Then came a "silent decade" of work with almost nothing published.

It ended in 1781 with the Critique of Pure Reason, when Kant was 57. The Groundwork of the Metaphysics of Morals followed in 1785, the Critique of Practical Reason in 1788 and the Critique of the Power of Judgment in 1790: four foundational works in nine years. His central move, often called a Copernican revolution in philosophy, reversed the question of knowledge: objects conform to the structure of the mind, not the other way round. He credited David Hume with waking him from his "dogmatic slumber"; see Hume vs. Kant.

He did it without leaving home. Kant lived his whole life in and around Königsberg and never married.

Kant among Cox's philosophers

Against the other philosophers in the table below, all rated in Cox's volume, Kant's raw ratings sit near the bottom. Read the table as a record of documentation as much as of ability.

Cox found that philosophers as a group averaged higher than any other field on both ratings. Kant's modest place inside that elite group mostly reflects the thinness of his childhood file, the point Cox herself made. For head-to-head context, Kant vs. Hegel sets the idealists side by side, and our ranking of philosophers by estimated IQ places every figure in one table. Neither Nietzsche nor Marx appears in Cox at all.

What the number leaves out

An IQ estimate for ages up to 26 describes a young man. Kant's defining work came three decades later. A rating built on school rank and a first book could not register the capacity that mattered most: the persistence to spend eleven years rebuilding the foundations of knowledge, then produce three major critiques in nine years. That is a test of sustained concentration no timed exam approaches.

How we assessed this

We read Kant's case study in a scanned copy of Cox's 1926 volume, including the AI and AII ratings and reliability grades, and her discussion of the 135 group. We checked dates against standard references. Corrected figures appear only as secondary tabulations, so we report them with that label. Where Cox's raw rating and the internet figure differ, we give the raw rating first.

Editorial standard: IQ figures for historical figures are retrospective estimates and are labeled as such; scores for living people appear only when the person disclosed them or a reputable outlet reported them. Corrections: contact the editors.