Descartes's Secret Notebook: A True Tale of Mathematics, Mysticism, and the Quest to Understand the Universe

by Amir D. Aczel

René Descartes (1596–1650) is one of the towering and central figures in Western philosophy and mathematics. His apothegm “ Cogito, ergo sum ” marked the birth of the mind-body problem, while his creation of so-called Cartesian coordinates have made our physical and intellectual conquest of physical space possible.

But Descartes had a mysterious and mystical side, as well. Almost certainly a member of the occult brotherhood of the Rosicrucians, he kept a secret notebook, now lost, most of which was written in code. After Descartes’s death, Gottfried Leibniz, inventor of calculus and one of the greatest mathematicians in history, moved to Paris in search of this notebook—and eventually found it in the possession of Claude Clerselier, a friend of Descartes. Leibniz called on Clerselier and was allowed to copy only a couple of pages—which, though written in code, he amazingly deciphered there on the spot. Leibniz’s hastily scribbled notes are all we have today of Descartes’s notebook, which has disappeared.

Why did Descartes keep a secret notebook, and what were its contents? The answers to these questions lead Amir Aczel and the reader on an exciting, swashbuckling journey, and offer a fascinating look at one of the great figures of Western culture.

Genres: Science, History, Nonfiction, Philosophy, Biography, Mathematics, Biography Memoir

288 pages, Paperback

First published January 1, 2005

About the author

Amir Aczel was an Israeli-born American author of popular science and mathematics books. He was a lecturer in mathematics and history of mathematics.

He studied at the University of California, Berkeley. Getting graduating with a BA in mathematics in 1975, received a Master of Science in 1976 and several years later accomplished his Ph.D. in Statistics from the University of Oregon. He died in Nîmes, France in 2015.

Reviews

[Valeriu Gherghel · Rating 2 out of 5]

Biografii lui Descartes au subliniat – şi nu o singură dată – faptul că filosoful francez a fost un ins foarte discret, retras, care a preferat mereu penumbra.

Unii au pus acest comportament ascuns şi mistificator pe seama simplei sale dorinţe de linişte. Alţii i-au aflat, în schimb, vom vedea mai jos, mobiluri mai adînci, mai întortocheate. Ei au imaginat adevărate „teorii ale conspiraţiei” pentru a-i explica discreţia și dorința de a nu fi deranjat la orice oră din zi și din noapte.

Se spune, de pildă, că Descartes nu păstra legătura cu lumea decît printr-un corespondent de încredere. Doar acesta ştia precis unde locuieşte şi numai el îl putea vizita (la anumite ore!). Se mai spune că Descartes menţiona adrese false pe scrisori, pentru a-i rătăci pe curioși. Se amintește, desigur, că a notat într-o lucrare timpurie o sintagmă care i-a devenit cu timpul deviză și mod de viață: „Larvatus prodeo”: Înaintez mascat / acoperit. Şi, în fine, că a crezut dintotdeauna în adevărul prestigiosului proverb: „Bene vixit, bene qui latuit”: Acela trăieşte bine / fără pericole şi griji /, care ştie să se ascundă / bine. Într-o lume de exhibiționiști și palavragii plini de sine, n-ar fi rău să-i urmăm îndemnul...

Amir D. Aczel vede în Descartes un rosacrucian pasionat de magie şi mistică, în linia gînditorilor Renaşterii. Un magistru în ocultism. Pentru a arăta că filosoful a fost negreşit un rosacrucian, Amir D. Aczel spune povestea încîlcită a unui carnet secret, păstrat după moartea lui Descartes de către un discipol pios - un anume Claude Clerselier -, carnet redactat într-o limbă codificată şi studiat abia în 1676 (la peste un sfert de veac după moartea filosofului!) de către Leibniz, care a transcris cîteva fragmente - în special, formule matematice.

Carnetul, fireşte, nu s-a păstrat. Au rămas doar notele sumare ale lui G. W. Leibniz. „L-am cercetat ani de zile, i-a mărturisit Claude Clerselier lui Leibniz, dar nimic din ce conţine, simboluri, desene, formule, nu are sens [pentru mine]”. Se pare că Leibniz a intuit misterul matematic, dar a refuzat la rîndu-i să-l divulge contemporanilor.

Din acest motiv, una dintre preţioasele formule a fost descifrată abia în anii '80 de către un savant francez. Minune! S-a vădit astfel că Descartes descoperise, cu muuult înainte de Leonhard Euler, o teoremă topologică. Ceea ce nu e exclus. Această teoremă ar reprezenta, firește, unul dintre „secretele universului”. Ceea ce nu rezultă din istoria carnetului pierdut este, totuşi, legătura dintre filosoful-matematician şi membrii Rosa Cruce.

Prin urmare, Descartes a avut o viaţă dublă. Pe de o parte, a contat în ochii prietenilor (cu care a corespondat intens) drept un filosof care, pentru a ajunge la „cogito”, s-a îndoit de orice, inclusiv de adevărurile eterne, stabilite din capul locului de Dumnezeu (care nici El nu le mai poate modifica). Pe de alta, Descartes a fost un rosacrucian tăinuit.

Dincolo de datele imediat verificabile, nimic din aceste construcţii ipotetice nu pare credibil. Nu e deloc obligatoriu ca un om ascuns şi solitar să facă parte dintr-o societate secretă. Care, pe deasupra, dacă e să-i credem pe specialişti, nici nu a existat vreodată decît în scripte și narațiuni. Concluzia acestei pseudo-recenzii este următoarea: nu vă încredeţi prea tare în biografi. Mai ales dacă biograful este un matematician șugubăț și vrea să vă ducă de nas.

[Christina Baehr · Rating 4 out of 5]

I understood exactly none of the mathematics, but if there’s one thing I took away very strongly from reading this story about Descartes’s mathematical discoveries (both published and secret), it’s that 17th century philosophers (the English word semantically overlapped at the time with what we today call scientists) expected the universe to be a solvable puzzle. Not in a reductionist way—they really did view the universe as art.

It seems weird to us today that Kepler might imagine planets tidily shaped like Greek polyhedrons, but to people coming from the late Renaissance, it was the random and irregular that caused surprise. There’s a lovely epilogue about cosmologists in 2001 positing a model of the universe in a corresponding shape, and of course the shocking thing to them was the symmetry. (I have no idea of this whole polyhedron universe idea is even a thing anymore.)

Honestly, if there’s one thing I miss about the premodern world (and there are plenty of things I don’t miss!), it’s this sense of living in an unfolding mystery, gasping at perfectly timed plot twists in a theologically and scientifically rich story. (Cue popcorn meme)

The other thing that tickled me was that one time Descartes locked eyes with a woman he knew once (he was “the one that got away”) in an inn courtyard and her boyfriend immediately challenged him to a duel based only on their obvious chemistry across a crowded public space. However, Descartes was actually an accomplished swordsman (he also fought off pirates once) and won, then courteously withdrew leaving the guy unharmed to the woman and saying something sweet about her beautiful eyes. The cute part here is that not only did this story survive in a version by Descartes, but it was corroborated by the same story being passed down in the woman’s family. So now I will always have the wonderful mental image of old Mme de Rosay in her rocking chair surrounded by her grandkids being like “did I ever tell you about the time I ran into Descartes…”

I’m looking forward to following this up with Tillyard’s short classic on the Elizabethan worldview.

[Simon Robs · Rating 3 out of 5]

Giving Descartes his due as precursor to Einstein via Leibnitz et al. His "secret" notebook(s) affirming the Copernicus/Galileo/Kepler mapping of the universe and fundamental [shapes] building blocks of matter as used in analytic geometry to describe same. But why and HOW could Descartes and Spinoza not have crossed paths having both lived in Holland at similar times sharing similar philosophical interests?

[Denisse · Rating 5 out of 5]

Rene Descartes is one of my favorite mathematicians. I love how he made the Cartesian coordinates that makes everything simplified like a number line in every format. He is also more than that. He is a famous personality in Psychology and Philosophy.
The Secret Notebook is a very good read that lets you think thoroughly about the world of Mathematics, and the Earth in general. It also talks about principles and other psychology-related critical thinking.

[Akrabar · Rating 3 out of 5]

The book was a trifle disappointing. The authors' Fermat's Last Theorem was much better. In this book on Descartes, the author digresses a lot (imho). The saving grace(s) is/are the first and the last chapter.

[Ensiform · Rating 2 out of 5]

A look at Descartes’ life and work, written in a very breezy, popular style that supposes almost no math or philosophy experience. This material is peppered by a lot of winking references to Rosicrucians, the Inquisition, and some melodramatic insinuations about Descartes hiding his greatest discoveries (the “secret notebook” of the title, which Leibnitz decoded right after his death, so it’s not exactly secret, is it?).

This is the third Aczel book I have read (after the okay The Riddle of the Compass and the more interesting Chance), and while the others were both flawed, especially in matters of historical record, those flaws were outweighed by the stories Aczel had to tell. In the case of this book, though, the engine that drives the book, its raison d’etre, is not to tell Descartes’ story but to embellish it into something Dan Brown might write, a potboiler of secret societies and death threats. It is a sham of false drama, which the story of one of history’s greatest intellects, who was deeply religious, created Western philosophy, served as a gentleman soldier, and mingled with royalty, simply does not need. The book is riddled with errors, mostly minor (Aczel describes the Rosicrucians’ symbol right above an illustration of it that is quite unlike his description), and also contains many errors of logic (Aczel says Descartes had nothing to fear from the Inquisition regarding his cosmological model, since it was “not valid,” as if that has anything to do with a challenge to the Church’s authority); but Azcel’s main sin is his constant obfuscation – what he insinuates by not telling all the facts. For example, one of the main “reveals” of the book is that Descartes thought of, and hid, what would become Euler’s formula about three-dimensional solids, when it seems to be commonly accepted by scholars that Descartes did not make the final connection to the finished formula. He makes absurd, silly claims about November 10 being “eerily significant” in Descartes’ life, ironically adding mystical numerology to the life of a logical thinker. The false drama grates after only a few pages (the chapters and chapter breaks all ending with hyperbolic cliffhanger questions, all of which come to nothing in particular). And it is packed with uninformative filler (Descartes stopped to rest his horses! He went to an inn that was popular! This inn had people in it! He rested! He picked up his horses!). The book is deeply disappointing, because a sensible biography of Descartes for the layman, with Azcel using his expertise to make the math clear, could have been a treasure.

[R.L. · Rating 3 out of 5]

English review below the Greek one...

ΤΟ ΚΡΥΦΟ ΣΗΜΕΙΩΜΑΤΑΡΙΟ ΤΟΥ ΝΤΕΚΑΡΤ
Εκδόσεις ΕΝΑΛΙΟΣ
ISBN: 9789605366032

Μου αρέσει που αυτός ο εκδοτικός οίκος επιλέγει βιβλία από καθηγητές και άλλους που καταπιάνονται με διάφορα θέματα και τα κάνουν προσιτά στο ευρύ κοινό. Κάποιες φορές όμως οι συγγραφείς και οι εκδότες τους προσπαθόντας να κάνουν ένα βιβλίο πιο ελκυστικό, το περιγράφουν με έναν τρόπο που χωρίς να είναι ψευδής, σε προδιαθέτει για κάτι διαφορετικό.

Το ίδιο συμβαίνει και με αυτό το βιβλίο. Στο μεγαλύτερο μέρος του, ο Aczel απλώς εξιστορεί τη ζωή του René Descartes. Βασίζεται στην επίσκεψή του στο μέρος που μεγάλωσε και το εκεί μουσείο που είναι αφιερωμένο σε αυτόν ως πηγή για την παιδική του ηλικία και κυρίως στην βιογραφία του Descartes από τον λόγιο και ιερέα Adrien Baillet που εκδόθηκε περίπου 40 χρόνια μετά το θάνατο του Descartes. Στην αρχή του βιβλίου ο Aczel αναφέρεται σε ένα κρυφό σημειωματάριο και στο ενδιαφέρον του Gottfried Wilhelm Leibniz να το διαβάσει και να το αποκωδικοποιήσει, αφήνωντας να εννοηθεί κάποιο μυστήριο στη συνέχεια της ιστορίας. Υπάρχουν κάποιες λίγες αναφορές και υποθέσεις για την αδελφότητα των Ροδόσταυρων και για το αν ο Descartes ήταν ή δεν ήταν μέλος της, συχνά βασιζόμενες σε πολύ έμμεσες ενδείξεις. Προς το πολύ τέλος του βιβλίου ο συγγραφέας επανέρχεται στο κρυφό σημειωματάριο και αποκαλύπτει τι περιείχε και γιατί και πως (ίσως) κρατήθηκε κρυφό. Υπάρχουν αναφορές στη φιλοσοφία και στο έργο του Descartes στα μαθηματικά, καθώς και αναφορές στο έργο και στη ζωή άλλων προσώπων που σχετίζονται άμεσα ή έμμεσα με το έργο και τη ζωή του.

Γενικά αισθάνθηκα ότι το βιβλίο στερείται προσανατολισμού και ότι ο συγγραφέας συχνά χάνεται στις σκέψεις του. Υπάρχουν πολλές υποθέσεις και παραφιλολογία καθώς και φανταστικές σκηνές εδώ κι εκεί ανάμεσα στην εξιστόρηση πραγματικών γεγονότων. Πάντα μου αρέσει η Ιστορία καθώς και να μαθαίνω για πρόσωπα και πράγματα και για διάφορους επιστημονικούς τομείς ακόμα κι αν δεν είναι το φόρτε μου (Μαθηματικά π.χ.), όμως θέλω ταυτόχρονα ένα βιβλίο να έχει μία ταυτότητα, ροή και ειρμό. Εδώ το βιβλίο πάσχει.

ΥΓ: Αρκετά τυπογραφικά, ορθογραφικά κτλ σε αυτή την έκδοση. Δεν είναι ότι δεν διαβάζεται, αλλά πάντα με εκνευρίζει αυτό στα βιβλία και δεν είναι η πρώτη φορά που συμβαίνει με τις Εκδόσεις Ενάλιος. Επιμελητή δεν έχετε;


I feel that the blurb of this book is kind of misleading and that while I enjoy reading and learning everything that has to do with History, people, events, various themes and subjects (even if they are not my strong point, eg maths), I still need a book to have an identity, decent pace and to make sense. This book lacks a direction and I felt that the author often got sidetracked and lost his plot and/or made lots of assumptions and took a wide berth from his original subject matter.

[Andres · Rating 4 out of 5]

A graceful mixture. The titular notebook, item M, is the focal point towards which the many strands in this book get weaved. This book covers Descartes' journey from birth to death, the many significant people, and historical events that interacted with Descartes. I got a lovely sense of the social and cultural issues and crises of his day, as well as a wealth of esoteric references that help reveal the world of thought and idea that Descartes and the intellectuals of his day were engaged with. Descartes' work and its relevance to the historical development of modern science, and philosophy is outlined and sampled enough for the layperson to understand and follow the story without going into the details of their content. I recommend this in particular for people interested in the person of Rene Descartes, or interested in the life of a unique and great thinker, or interested in a story that follows one the most famous and important persons of a mostly forgotten place and time that influenced the creation of the modern world. Illuminating.

[Christos Bouras · Rating 4 out of 5]

Εξαιρετικό. Ο Amir Aczel με σημείο αναφοράς τον Καρτέσιο σκιαγραφεί μια σκοτεινή εποχή πολέμων, θρησκευτικού φανατισμού, αντιζηλίας μεταξύ επιστημόνων. Στο επίκεντρο ο τεράστιος φιλόσοφος και επιστήμονας Καρτέσιος μοναχικός, σε μια συνεχή κίνηση για να αποφύγει την πιθανότητα να διωχθεί, σε μια αέναη μάχη για το τι πρέπει να δημοσιεύσει και τι να κρύψει. Ο Καρτέσιος στην εποχή των θρησκευτικών πολέμων στην Ευρώπη περιπλανιέται και γράφει. Παρίσταται σε κοσμοϊστορικά γεγονότα και συνομιλεί με σημαντικούς ανθρώπους. Κρύβει μεγάλο μέρος της συγγραφικής παραγωγής από τον φόβο της καταδίκης όπως στην περίπτωση τους Γαλιλαίου.
Από το εξαιρετικό αυτό βιβλίο παρελαύνουν μεγάλοι επιστήμονες που επηρέασαν η επηρεάστηκαν από τον Καρτέσιο όπως ο Κέπλερ, ο Γαλιλαίος, ο Λάιμπνιτς, ο Νεύτων. Παρελαύνουν και ξεχωριστές γυναίκες όπως η πριγκίπισσα Ελισάβετ της Βοημίας και η Χριστίνα της Σουηδίας. Γύρω από όλους αυτούς το έργο και ο χαρακτήρας μυστικοπαθείας του Καρτέσιου κυριαρχούν, του ανθρώπου που όρισε την σύγχρονη επιστημονική σκέψη.

[Tom Carrico · Rating 4 out of 5]

Descartes’ Secret Notebook
By Amir D. Aczel

Reviewed by Tom Carrico

This fascinating and highly readable book is part biography, part mystery and part treatise on philosophy and mathematics. Rene Descartes lived from 1596 to 1650. His life was one of adventure and discovery. His philosophy was hotly debated at the time and his discoveries in mathematics were and are regarded as genius. This author tries to add another layer to the legend by examining a purported “secret notebook”, long lost but copied in part by German mathematician Gottfied Wilhelm Leibniz after Descartes’ death.

Rene Descartes was born to a wealthy family in the town of Chatellerault, France. He was baptized in the Roman Catholic Church and remained a devout and loyal Catholic his entire life. His mother died in childbirth a year later and Descartes’ own health as a youth is described as poor. He received what we all recognize as the great advantage of a Jesuit education (Hoya Saxa! – but we digress) at what is now a military academy in the town of La Fleche, the Prytanee National Militaire. He then received a doctor of laws degree in 1616 and moved to Paris. In Paris he developed his interests in mathematics, physics and eventually, philosophy. He also traveled extensively to the Netherlands and Denmark. His health as an adult was much improved and he never lost his interest in the military. He even joined the army of Maximilian, the duke of Bavaria, at the beginning of the Thirty Years War. It was during this time as a volunteer soldier in Maximilian’s army that he began his studies and interpretations of geometry and science. Eventually Descartes settled in Holland where his Cartesian philosophy created controversy. Everyone is familiar with the “I think, therefore I am” (or “Cogito, ergo sum.”), but the basis for this definitive statement is a very concise, even mathematical, proof of the existence of God. This was the time of turmoil between the Roman Catholic Church and the Protestant denominations and the acceptance of Descartes’ reasoning was not universal. He was even accused of the serious charge of atheism despite his devout Catholic heritage and practice. Eventually Descartes became the philosophy instructor for Queen Christina of Denmark. There were jealousies between Descartes and the Queen’s other instructors, as Descartes quickly became the young Queen’s favorite. The fact that the others were strict Calvinists played a role. Descartes died under somewhat suspicious circumstances in Sweden in 1650. There are suggestions that he may have been poisoned by a rival. His belongings were catalogued and shipped to relatives in France. Eventually many of his original documents, including the “secret notebook” alluded to in the book’s title, disappeared.

The secret notebook was a private notebook which Descartes never intended to publish. He used codes and symbols that were indecipherable for centuries. Part of this notebook was copied by Leibniz shortly after Descartes death and that is all that remains of the document. Some historians felt that this notebook represented Descartes membership in a secret society, the Rosicrucians. Others felt that Descartes had discovered the origins of the universe. It was not until 1987 when Pierre Costabel published his definitive analysis of Leibniz’ copy of Descartes’ secret notebook that the true meaning of the secret notebook was revealed. Descartes had discovered a coveted formula for a rule which governs the structure of three dimensional solid objects. This was mystery which had eluded Plato and the other Greek geometricians as well as all other mathematicians in history. He had discovered the modern field of topology centuries before its time. The reason he repressed this discovery was because it supported Kepler and Copernicus and their analysis of planetary motion around the sun. The timing of this coincided with the Roman Catholic Church’s prosecution of Galileo for heresy. Descartes, the loyal Catholic, did not want to suffer the same fate.

There are many interesting side stories in this tale, including the simultaneous discovery of the calculus by Newton in England and Leibniz in Germany. There may be a connection between these two men which would be, of course, Rene Descartes. Descartes private life is examined as far as historical facts allow, including a possible marriage to a servant girl and a relationship of some sort with Princess Elizabeth of Bavaria who was living in exile in Holland at the same time as Descartes. The exact relationship between Descartes and Queen Christina is a mystery as well. At about age 40, Descartes noticed his first grey hairs. He felt this was a sign of impending death and began dissecting animals by the hundreds in an attempt to discover the secret to a prolonged life. He greatly altered his diet, becoming basically a vegetarian.

This is a fascinating book. I remembered very little of Descartes from my Philosophy 101 class and this book made me wish I had paid more attention. The historical aspects of this time are equally absorbing. The author makes the mathematics understandable (not an easy task in my humble opinion) and the philosophy enjoyable. Descartes’ Secret Notebook by Amir D. Aczel is available in trade paperback from Broadway Books.


Next Month: This year marks the 200th anniversary of the birth of Edgar Allan Poe. We will start looking at the 2009 Edgar Award nominees for best mystery novel of the year, but I will start with a review of Peter Ackroyd’s new biography of Poe.

[Andrew · Rating 2 out of 5]

Eminently readable, totally empty. For much of the book I thought the shallowness I was sensing was due to my mathematics background. But that thin sketching is visible in all areas—Aczel doesn't do a very good job of elucidating the matter or meaning of Descartes's work in mathematics or philosophy, outlining the relevant religious and political history of Europe, untangling the myths surrounding the Rosicrucians, or assembling Descartes's biographical details. Despite doing basically nothing it sets out to do to a satisfactory degree, I'm only going 2 stars instead of 1 because it isn't actively grating.

[Rick Sam · Rating 4 out of 5]

I took this book from Reston's Used Book Store, VA. Interesting, the owner of the store did not have old scientific/philosophical or engineering books.

I found fascinating stories and letter of Descartes.

One Story: Malebranche first read Descartes philosophy in a manuscript. He did become so excited that he suffered from palpitations of the heart. This is funny; I laughed so loud.

Leibniz read Descartes manuscripts, and so did Newton. Overall, I'd recommend this book to fans of Philosophy

--Deus Vult
Gottfried

[Christopher Fuchs · Rating 5 out of 5]

This was a very enjoyable book, a light beach or cabin read for those looking to relax but still scratch the curiosity itch. The mysterious and very accomplished life of philosopher and mathematician Descartes still fascinates people, and Aczel—a mathematician and prolific author himself—provides well-researched storytelling that sometimes reads theatrical. Aczel’s book is a satisfying walk through the life, influences, dangers, and legacy of Descartes, whose work still influences many fields of study and practical use today.

[RA · Rating 4 out of 5]

A biography of Descartes, with the main focus somewhat on his secret writings. There is definitely some commercial tilt in its structure and the author, a mathematician by training, seems not a great story teller. For me it was the first biography of Descartes the man, and from it one cannot but admire the scientist and the philosopher, and understand a bit the man. From the pages of the book Descartes emerges as one of the giants on whose shoulders Newton stood. Neither thrilling, nor boring. I would be tempted to read his other books.

[Ivan · Rating 5 out of 5]

This is a beautifully written short biography of Descartes. It offers a glimpse into the Enlightenment world of the 17th century. There are also some well integrated detours presenting other relevant people and events. For me the book was a real page-turner.

On the downside, it does not go into any detail about Descartes philosophy. For this you can read Nadler's "The philosopher, the priest, and the painter".

[Phillip Ramm · Rating 2 out of 5]

The titular secret notebook didn't get much emphasis, this was more of a superficial biography and very light assessment of Descartes' philosophy and mathematical achievements. I came away not really understanding, or being convinced why Descartes should be so revered in scientific and philosophical circles. I think, therefore I am unimpressed.

[Edward Westerbeke · Rating 3 out of 5]

This was two books in one. The first was about Descartes life which I enjoyed very much. The latter was about his secret notebook which was a difficult read as it was an explanation of his mathematics and the discovery of calculus. I did not get much out of that. I should have skipped that part.

[Amanda · Rating 3 out of 5]

Well-written bio of a fun dude. A good read for a abridged experience of Baillet's bio of Descartes. Not as much on his actual philosophies and the math as I would've liked; the primary focus was on his experiences and relationships etc.

[Ron Me]

It's a biography dressed up to seem like a mystery novel, doubtless with the intention of reaching a less literate audience. Passable. But I have a copy of Descartes' Philosophical Works I used in college (in translation) and I won't be keeping this.

[Chris Craddock · Rating 5 out of 5]

McDonalds wifi ate my review then asked if I wanted fries with my order. No thanks.

[D. Meador · Rating 3 out of 5]

Interesting, never realized Descartes’ contemporaries or the actual time period.

[Grant Swartz · Rating 4 out of 5]

Amazing

[Christopher Heckman · Rating 3 out of 5]

A bit wordy, although it does clear up a few myths about DeCartes.

[Emg · Rating 2 out of 5]

The simple declarative sentences drove me nuts. Really needed some variety in structure. There was no explanation of the math which was frustrating on occasion.

[Javier Galeano · Rating 4 out of 5]

El libro cuenta la vida de Descartes, teniendo en cuenta sus descubrimientos. El libro es bastante entretenido y te da una visión bastante completa del filósofo y matemático francés

[Peter van de Pas · Rating 2 out of 5]

One thing I'd like to add to all the comments. Aczel tells us that Descartes learned the language 'Flemish' while living in Breda (the place I was born) but Flemish is, and was, the term used for the version/dialect of Dutch that is spoken in what is now Belgium. Breda is not located in Belgium, but in The Netherlands and the dialect spoken in Breda is Brabantian. When you're in Breda the language you want to learn is Dutch.
Further on in the book he states that when Descartes was visiting the Frisian Islands he saved himself from a violent robbery because he could understand what his shipmates were saying about him in their dialect and could answer them back perfectly in that dialect, all because he had learned to speak Flemish. First of all, Frisian is a seperate language from Dutch. Secondly, there is no way a native speaker of Dutch, especially one hailing from the south, where Breda is located, could understand a word of the Frisian dialect, let alone speak this perfectly. They are as far apart as French and Italian. How a, admittedly very gifted, second language speaker could pull this off is a mystery to me.
If this reflects the level of inquiry that preceded the writing of this book then anything in there could be false. I recommend reading other books on Descartes.
Oh, and by the way, only the last 30 pages or so are about this 'secret' notebook, the rest is a rather shallow mini-biography of Descartes.

[V · Rating 2 out of 5]

(Spoilers) I picked up this book presuming that the entire novel was a thrilling cross-analysis of the full secret notebook of Descartes and a revelation of his deceptive deeds. Unfortunately, this is not the case. This book is simply a biography of Descartes, mainly due to the fact that his "secret notebook" (only 16 pages long) was never again found after the 1700s & unable to be fully analyzed. The only fragment left of his notebook is a short & scribbled written copy of a couple pages from 1676 by a mathematician named Leibniz who was once allowed to see the notebook for some brief hours. At the end of this novel, you discover that Leibniz decoded one of Descartes' theorems in the notebook which scientists today claim is "completely wrong" and quite useless.

In addition, if you're hoping for Descartes to have been a scruffy and anarchic crusader of the truth, you'll also be disappointed. Descartes wore silky gloves and feathered hats while coaxing the church. He made every effort possible to distance himself from secret societies and his vivacious friends. One thing, however, that he had no problem with was jumping from country to country like he did from lover to lover.

All in all, I found the book to be easy to read and quite insightful. I learned about the European politics of that era, the religious crusades between the Catholics and Protestants, and about other key mathematicians before and after Descartes.

[Whoof]

Found it quite amusing and entertaining, but some of the mathematical exposition (and there isn't too much of it) seems misleading.

I think most of what I learned from reading this (outside of interesting biographical details of Descartes) needs to be double-checked for veracity. Aczel essentially asserts that Descartes' secret notebook contained Euler's formula (F+V -E = 2) but poking around some other sources reveals that it isn't so simple, although Descartes had derived a related and near equivalent formulation--but not *quite* so clear cut as Euler's! Aczel could have been more specific about what was actually inside of Descartes' "secret" notebook, as this is the climax the book builds up to. As it is it feels misleading. The bit about Descartes' square root construction being something unknown to Euclid may also be untrue.

However, I will say that despite parts of this book being historically inaccurate, it never feels like it is *trying* to tell the full truth, and thus I read the whole thing with a grain of salt anyway. This is largely because of the funny mystical society bits, which the author covers with a "whooo knooowws the truutthh??? woooooooooo" kind of tone. Again, I found this amusing more than anything, and it made me take everything in the book as a possible half-truth. So there might a redeemable quality to the inaccuracy? In any case, it motivates further investigation, so that's good, I guess.

Odd book.

[Tom · Rating 4 out of 5]

I really enjoyed this book. All I really knew about Descartes before this was "cogito ergo sum" and that he is commonly attributed with dividing the mind from the body in Western philosophical thought. He was much more interesting that just those two tidbits. If he wasn't actually a member of the Rosicrucians, he was certainly in correspondence with that very secret group and heavily influenced by their thinking...hence the secret notebook.

Descartes married geometry and algebra and thereby laid the groundwork for modern science. The Cartesian coordinate system is part of the normal high school math curriculum and necessary for understanding science. Descartes wanted to go beyond the simple two dimensional framework that this allowed, but the math wasn't available for another several centuries.

Liebniz the famous mathematician was able to get a peak at D's secret notebook (since lost) and was able to grasp the great 'secret' that it contained. The fact that it, in part, confirmed the heliocentric worldview of Copernicus, and therefore ran counter to the teachings of the Church, coupled with the reality that Europe was embroiled in the Thirty Years War, accounts for why D kept this secret. People were sent to the stake for far less.

The book is very well written and complicated concepts clearly explained.

[Barbara · Rating 4 out of 5]

I really enjoyed this book. I'd seen it in a library display and thought it might be interesting....Not my usual type of reading at all, but I'm very glad I read it.

The book was mostly a biography of Descartes. Some of it was familiar to me, from learning about Descartes in French class and reading Discourse on the Method that J inspired me to study. It was enjoyable reading about the Rosicrucians, taking me back to my years as an astrologer. Pythagoras, Hermes Trismegistus, Tycho Brahe, Max Heindel--familiar names from long ago metaphysical studies. Fascinating, too, to read about Descartes' association with Queen Christina.

When it came to the more mathematical/scientific discussion of his work and the contents of the secret notebook, I was a bit out of my depth. I've forgotten what little I ever knew of math. I think the author did a good job of making it (fairly) understandable to the lay reader. I got enough out of the explanations to leave me impressed by Descartes' thinking.