Mary Somerville

Somerville's dominant function was Ti — introverted thinking — and it expressed itself in a form unusual even among scientists: she was not primarily interested in discovering new phenomena but in understanding the logical structure that organized existing ones. When she translated Laplace's Mécanique Céleste for The Mechanism of the Heavens, she did not merely render the French into English. She rewrote it — expanding the mathematical demonstrations, adding physical context, reconstructing proofs from first principles when the original presentation seemed to her insufficiently rigorous. The work was nearly twice as long as the original because Somerville could not leave a logical gap unfilled.

This is Ti at its most characteristic: the drive to achieve internal consistency, to close all the logical loops, to understand not just what the answer is but why the answer must be exactly that and not something else. Somerville described her intellectual method in her autobiography with characteristic directness — she worked through problems multiple times, from different angles, until she was satisfied that she genuinely understood rather than merely knew. The distinction mattered enormously to her. Memorization without comprehension was the kind of learning she despised; it was, in her experience, what society offered women as a substitute for real education.

Her self-education, which began in childhood and continued into her eighties — she published her last book at eighty-nine — was itself a Ti project. She identified the gaps in her understanding, found the texts that could fill them, worked through them systematically until the understanding was genuine, and then moved on to the next gap. She learned without teachers for most of her life not because no teachers were available but because the self-directed construction of understanding was how her mind actually worked.

Her Ne auxiliary — extraverted intuition, the function that perceives connections and possibilities across apparently separate domains — is what made Somerville's scientific project possible. The thesis of On the Connexion of the Physical Sciences was not that science had many branches but that those branches were ultimately expressions of a single underlying reality, and that the relationships between them were as important as the facts within each. Astronomy, mathematics, magnetism, electricity, physics, geography — Somerville saw them all as facets of a single coherent system, and her Ne was the function that kept generating the connections: this equation in celestial mechanics has the same structural form as this phenomenon in electromagnetic theory; these tides are the same force as these stellar motions.

Ne in the INTP is the restless outward-facing complement to Ti's internal depth. Where Ti wants to understand one thing completely, Ne keeps producing new things to understand — new angles, new domains, new applications. In Somerville's life, this expressed itself as a genuine polymathism that was not scattered but cumulative: each new domain she mastered added to the conceptual web rather than replacing what had come before. She moved from algebra to calculus to celestial mechanics to physical geography to the physical sciences broadly, and at each stage she brought everything she had previously understood with her.

It was precisely this Ne-driven synthesis that produced one of the nineteenth century's more remarkable near-misses: a footnote in the 1842 edition of On the Connexion of the Physical Sciences, in which Somerville speculated about unexplained perturbations in the orbit of Uranus and suggested they implied the existence of an undiscovered planet. John Couch Adams and Urbain Le Verrier both read that passage; one of them acknowledged it directly. The planet Neptune was discovered in 1846.

Si tertiary in the INTP provides the grounding in accumulated experience and methodical accumulation of detail that prevents the Ti-Ne axis from becoming purely abstract. For Somerville, Si expressed itself as extraordinary scholarly discipline. She was not a genius of sudden inspiration; she was a genius of patient, meticulous construction. Her mathematical self-education as a child and young woman was conducted by working through textbooks problem by problem, building understanding brick by brick. Her later research involved decades of accumulated reading across multiple scientific fields, held in memory with remarkable fidelity.

She revised her books meticulously across multiple editions — On the Connexion of the Physical Sciences went through ten editions in her lifetime, each updated to reflect new scientific developments. This is not the behavior of someone whose relationship to existing knowledge is casual. Somerville treated the accumulated body of scientific understanding with the same care she gave her internal logical frameworks — it mattered to get it right, to track changes, to maintain precision across time.

Her Si also appears in what she valued about her work: accuracy and completeness. She was not primarily interested in credit, novelty, or recognition. She wanted to explain things correctly. When she discovered errors in earlier editions, she was distressed rather than indifferent. When reviewers praised her synthesis but found minor inaccuracies, she corrected them before the book went to press again. The standard she held herself to was internal, not social — a mark of the Si tertiary providing backup for the Ti dominant's drive toward truth.

The Fe inferior of the INTP — extraverted feeling, the function least naturally available to this type — is not an absence of warmth but a particular vulnerability: a tendency to underestimate the social dimensions of situations, to be surprised by emotional reactions, to feel somewhat alien in purely social contexts where logical considerations take a back seat. For Somerville, this expressed itself most visibly in how she navigated the recognition that came with her scientific achievements.

She was genuinely surprised when The Mechanism of the Heavens made her famous. She deflected credit reflexively — crediting Laplace, her husband William, her colleagues. When she and Caroline Herschel were elected the first female members of the Royal Astronomical Society in 1835, she wrote that she was embarrassed and felt unworthy. This was not false modesty; it was the Fe inferior expressing genuine discomfort with social valuation of work that had been, for her, internally motivated. She had not written to be recognized; she had written to understand and to explain. The recognition felt like a response to something other than what she had been doing.

Her first marriage — to Samuel Greig, son of the Kronstadt admiral — may also illuminate the Fe inferior. She married young, to a man who disapproved of her studies, and endured several years of intellectual suppression before his death freed her. The INTP can underestimate the degree to which their environment shapes their psychological health; Somerville's explosion of productivity after Greig's death and her subsequent partnership with William Somerville suggest that she required, but had not initially chosen, a relationship genuinely supportive of her intellectual life. Once she had it, she never looked back.

Why INTP Over INFP or ENTP

The essential distinction is between logic as a tool and logic as a home. For the INFP, the inner world is organized by values; for the ENTP, ideas are exciting because they open possibilities. For Somerville, the internal logical framework was the primary reality — the thing she was actually building when she worked. The mathematics was not a means to an end; it was the thing itself. That orientation — Ti as the primary cognitive mode — makes her unmistakably INTP.