Short answer: Only one scholarly source ranks philosophers by estimated IQ: Catharine Cox's 1926 study of 301 geniuses born between 1450 and 1850. On her raw ratings, Gottfried Leibniz (185 in childhood, 190 as a young adult) and John Stuart Mill (190, then 170) lead, and Immanuel Kant received 135 and 145. Socrates, Plato, Aristotle, Pythagoras and Thomas Aquinas were born too early to be rated. Nietzsche and Marx were born in time but left out.
At a glance
| Scholarly source | Catharine Cox, The Early Mental Traits of Three Hundred Geniuses (Stanford University Press, 1926) |
|---|---|
| Who it covers | 301 eminent people born 1450–1850 |
| Top early-adult rating in our table | Gottfried Leibniz, 190 |
| Top childhood rating in our table | John Stuart Mill, 190 |
| Ancient philosophers with estimates | None |
| Born in Cox's window but unrated | Friedrich Nietzsche, Karl Marx |
| What the numbers are | Retrospective ratings of biographical records, not test scores |
The ranking: every philosopher IQ page in one table
Ranked honestly, the list is short. Of the eight philosophers with full IQ analyses on this site, one has a scholarly estimate. The other seven sit outside the only study that produced such estimates, either because they were born before 1450 or because Cox's selection rules passed them over.
| Name | Estimate | Basis |
|---|---|---|
| Immanuel Kant | 135 (childhood); 145 (ages 17–26) | Cox (1926) raw ratings on data graded .43 for reliability; tables of her corrected figures give about 175 |
| Socrates | No scholarly estimate | Born c. 470 BCE, long before Cox's 1450 start; wrote nothing himself |
| Plato | No scholarly estimate | Born in the 5th century BCE, outside Cox; popular figures are speculative |
| Aristotle | No scholarly estimate | Born 384 BCE, outside Cox; the evidence is his surviving work |
| Pythagoras | No scholarly estimate | Born in the 6th century BCE, outside Cox |
| Thomas Aquinas | No scholarly estimate | Born c. 1225, outside Cox; eight million words of output on record |
| Friedrich Nietzsche | No scholarly estimate | Born 1844, inside Cox's window, but not among her 301 subjects |
| Karl Marx | No scholarly estimate | Born 1818, inside Cox's window, but not rated |
That is not a failure of research. It is the state of the evidence. Every number beyond Kant's that circulates for these eight has no named estimator and no published method. The method behind the one real figure is explained in our guide to historical IQ estimates.
Cox's philosophers: the only real estimates
Cox's 1926 volume holds case studies for many of the modern philosophers. Each received two ratings: an AI IQ for development to age 17 and an AII IQ for ages 17 to 26. The table below ranks eight philosophers we checked against the case headings in her book, ordered by the early-adult figure.
| Rank | Philosopher | Childhood (to 17) | Early adult (17–26) |
|---|---|---|---|
| 1 | Gottfried Leibniz | 185 | 190 |
| 2 | Blaise Pascal | 180 | 180 |
| 3 | John Stuart Mill | 190 | 170 |
| 4 (tie) | David Hume | 155 | 160 |
| 4 (tie) | René Descartes | 150 | 160 |
| 6 (tie) | G. W. F. Hegel | 150 | 145 |
| 6 (tie) | Immanuel Kant | 135 | 145 |
| 6 (tie) | Baruch Spinoza | 130 | 145 |
Leibniz leads on the adult figure; Mill posts the highest childhood rating, 190, backed by an unusually well-documented childhood. Pascal, a mathematician as much as a philosopher, rated 180 on both. Leibniz and Pascal also appear in our ranking of mathematicians by estimated IQ.
Cox's broader finding favors the field. In her words, "the average for the young Philosophers is higher for both the AI and the AII IQ's than the corresponding average of any other group." Soldiers scored lowest. Part of the gap is documentation: across her sample, the more reliable the data, the higher the estimate, and philosophers left fuller records than soldiers. Cox still judged the difference between the groups genuine.
How the 1926 estimates were made
Cox began with James McKeen Cattell's list of the 1,000 most eminent people in history, ranked by the space each received in biographical dictionaries. She dropped hereditary aristocrats and anyone born before 1450, struck names ranked below 510th, and set aside cases with no usable records. That left 282 subjects. She added 19 more from further down Cattell's list, for 301.
For each subject she compiled a dossier on childhood and youth: family, schooling, reading, early writing, class rank, first publications. Raters converted each dossier into an estimated IQ pegged to the Stanford revision of the Binet-Simon scale, the test Lewis Terman introduced in 1916, which expressed IQ as a ratio of mental age to chronological age. Cox also graded how reliable each dossier was. Kant's, for example, scored .43.
Two consequences follow. Early bloomers with attentive families score high. Late bloomers with sparse records score low, whatever they later achieved.
Raw ratings vs. the bigger numbers online
Some of the higher figures online trace to Cox's second step. She knew thin records dragged every rating toward the average, and wrote that removing that effect "would raise all of the scores far above their present positions." Her correction produced larger numbers, which she treated as rough lower bounds, not measurements. Kant's corrected figure, as reproduced in secondary tables, is about 175, against raw ratings of 135 and 145.
Lists that mix raw and corrected figures without saying so make comparisons meaningless. A corrected 175 for one philosopher beside a raw 145 for another says nothing about who was brighter. When comparing, use the same column for everyone. This ranking uses the raw ratings Cox printed in each case study.
Neither kind of number is a modern IQ. Today's tests report deviation scores with a mean of 100 and a standard deviation of 15, and the adult Wechsler scale tops out at 160. Figures such as Leibniz's 190 belong to a different, older system of estimation.
Why the ancients have no numbers
The founders of Western philosophy are the least measurable people on the list. Socrates wrote nothing; his mind reaches us through Plato, Xenophon and Aristophanes. Plato and Aristotle left large bodies of work but no dated childhood record. Pythagoras is known mainly through reports written long after his death. Thomas Aquinas, born around 1225, left eight million words but no school reports.
Cox's method needs exactly what these lives lack: evidence of what the subject could do at 8, at 12, at 20. Popular figures of 170 to 200 for the Greeks are inferences from reputation and breadth of work, not ratings of evidence. Our individual pages set out what the evidence does show, from Aristotle's founding of formal logic to the oracle story that named no one wiser than Socrates. For achievement-based rankings, see the greatest philosophers of all time.
The missing moderns: Nietzsche and Marx
Two of the best-known modern philosophers were born inside Cox's window and still have no rating. Karl Marx was born in 1818 and Friedrich Nietzsche in 1844. A full-text search of her volume finds neither name. Whatever the reason, neither made her final roster, so no one ever built their dossiers.
The documented records are strong on their own terms. Nietzsche held a chair in classical philology at Basel at 24, before completing a doctorate. Marx took a doctorate from Jena in 1841 and left a collected works of 50 volumes, shared with Engels. Neither fact converts into an IQ.
What any philosopher IQ ranking misses
An IQ ranking of philosophers is partly a ranking of documentation. Mill's childhood file is among the fullest in Cox's book; Kant's teachers, by her account, suspected nothing special. The ratings reflect that difference as much as any difference in mind.
It also measures the wrong period for many thinkers. Cox's ratings stop at 26. Kant published the Critique of Pure Reason at 57. Philosophy rewards decades of sustained work on a few problems, which no timed test and no rating of youth can capture. Read the numbers as one line of evidence, never as the verdict. The full field of great thinkers, ranked by influence, is on our greatest philosophers list.
How we built this ranking
We read the case headings in a scanned copy of Cox's 1926 volume to confirm each rating in the tables, checked her selection rules and her remarks on philosophers, and ran full-text searches for thinkers who do not appear. Where a philosopher has no scholarly estimate, we say so rather than borrow an unsourced figure. We will add rows when new peer-reviewed estimates appear.
Frequently asked questions
Which philosopher had the highest IQ?
On the only scholarly estimates, Catharine Cox's 1926 ratings, Gottfried Leibniz leads for early adulthood at 190, and John Stuart Mill has the highest childhood rating at 190. These are retrospective estimates from biographical records, not test scores, and they cover only people born between 1450 and 1850.
What was Plato's IQ?
Plato has no scholarly IQ estimate. He lived in the 5th and 4th centuries BCE, far outside Cox's study of people born from 1450 to 1850, and left no dated record of his childhood development. Figures online are speculative. See our Plato IQ analysis.
Are philosophers smarter than other geniuses?
In Cox's 1926 study, philosophers averaged higher estimated IQs than any other field on both of her ratings, and soldiers averaged lowest. Philosophers also left fuller records, and in her data fuller records produced higher estimates, though Cox judged the difference between fields genuine.
Why do online lists give ancient philosophers IQ scores?
Because demand for a number is high, and fame is easy to convert into one. No scholarly method has ever produced an IQ estimate for Socrates, Plato, Aristotle or Pythagoras. Figures attached to them lack a named estimator and a stated method, which is the minimum any historical estimate needs.
Who is the smartest philosopher of all time?
No data can settle it. The ancients were never rated, and Cox's ratings favor philosophers with well-documented childhoods. On her numbers, Leibniz and Mill rank highest among modern philosophers. Rankings by influence answer a different question, about achievement rather than IQ; our greatest philosophers list takes that approach.
Sources
- Cox, C. M. (1926). Genetic Studies of Genius, Vol. II: The Early Mental Traits of Three Hundred Geniuses — Internet Archive — Case-study ratings for Leibniz, Pascal, Mill, Hume, Descartes, Hegel, Kant, Spinoza; selection rules; philosophers' group average; correction method
- Simonton, D. K. — Personal characteristics that contribute to greatness (chapter reproducing Cox's estimates), UC Davis — Secondary tabulation of Cox's uncorrected and corrected estimates for philosophers
- Catharine Cox Miles — Wikipedia — The 1926 dissertation on 301 geniuses as Volume II of Terman's Genetic Studies of Genius
- Socrates — Stanford Encyclopedia of Philosophy — Socrates wrote nothing; sources in Plato, Xenophon, Aristophanes
- Friedrich Nietzsche — Stanford Encyclopedia of Philosophy — Basel chair at 24
- Karl Marx — Wikipedia — Birth 1818 and 1841 Jena doctorate
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.
