Elementary, my dear friends: Euclid of Alexandria makes mathematics interesting and fun.
Not much is known about Euclid. The editors of the edition of The Elements that I have before me indicate that “Euclid appears to have lived in the time of the first Ptolemy, 323-283 B.C., and to have been the founder of the Alexandrian school” (p. 253). But his importance as a mathematics scholar and educator has been recognized since his time – as demonstrated by the way in which, in Raphael’s classic painting The School of Athens (1511), with its all-star lineup of great thinkers from classical Greece, one can see Euclid teaching mathematics to some young pupils. Look at that portion of the painting, next time you’re at the Vatican Museum, and no doubt you will find it engaging – as I did – that Euclid’s students are finding all his math talk interesting, in spite of themselves.
Euclid’s work is best known to people of the modern world through his treatise The Elements, in which he sets forth principles of what has come to be known as Euclidean geometry. Math – or “maths,” if you are from Great Britain – will never be my strong suit; but I found that my time reading The Elements gave me a strong sense of what mathematics aficionados love about math (or maths).
First, a few words about organization (and that sounds very math, doesn’t it?) The Elements is divided into 12 books; but, as the editors of this J.M. Dent & Sons/Everyman’s Library edition of The Elements helpfully explain, most modern readers who come to Euclid’s work in the hope of gaining in mathematical knowledge and/or cultural literacy in a general way only read Books I-VI, Book XI, and a bit of Book XII. If you want to seek out the rest of the books, with all their pages and pages, then you’re a better mathematician than I (not heavy lifting, that).
Each book of The Elements focuses on a different area of mathematics: Book I is dedicated to triangles and parallelograms; Book II to lines, segments, and rectangles; Book III to circles, and so on. Within each book, one will typically find definitions, postulates, axioms, theorems, and problems. In case you weren’t sure:
• A postulate is an assumption of the truth of something, as a basis for discussion.
• An axiom or common notion is a statement that is accepted as true, without needing to be proven. In other words, it is self-evident.
• A theorem is a statement that is not self-evident, but that can be proven to be true. Each proof of a theorem is followed by the initials Q.E.D. (Latin, quod erat demonstrandum, meaning “that which was to be demonstrated”).
• A problem is an opportunity to work out, on one’s own, the ideas that have been set forth and proven in a theorem. Each solution of a problem is followed by the initials Q.E.F. (Latin, quod erat faciendum, meaning “that which was to be done”).
Ordinarily, when reviewing a book, I will try to pick out some key passages from said book, so that you, friend reader, will have a sense of the content of the book as well as its style and tone. But I’m not sure that doing so will work so well in the case of Euclid and The Elements. Consider, for example, Book I, Proposition 47 (a theorem): “In any right-angled triangle, the square which is described on the side subtending the right angle is equal to the squares described on the sides which contain the right angle” (p. 50).
Are you with me so far?
How about Book III, Proposition 28 (another theorem): “In equal circles, equal straight lines cut off equal arcs, the greater equal to the greater, and the less equal to the less” (p. 100).
Hey, did somebody say, “Keep on rockin’?”
Or we could try Book V, Proposition 9 (yet another theorem): “Magnitudes which have the same ratio to the same magnitude, are equal to one another; and those to which the same magnitude has the same ratio, are equal to one another” (p. 150).
I got blisters on my fingers!
Finally, consider Book VI, Proposition 20 (one final theorem): “Similar polygons may be divided into the same number of similar triangles, having the same ratio to one another that the polygons have; and the polygons are to one another in the duplicate ratio of their homologous sides” (p. 200).
Am I buggin’ ya? I don’t mean to bug ya.
You get the idea. Quoting a theorem in isolation fails to convey what is so helpful and enlightening about reading The Elements (and, by the way, extra points to all who got all of the classic-rock allusions that I jotted down in response to each of those theorems).
The way that Euclid proceeds from definitions, axioms, and/or postulates to theorems and problems guides the reader through the process with admirable clarity. And this Dent/Everyman’s Library edition provides illustrations on every page, for every theorem or problem. I found myself drawing lines on scratch paper of my own, working out what Euclid had done to demonstrate a theorem or solve a problem. I found that Euclid makes math make sense.
And there’s one more reason why Euclid and The Elements should be important to you, even if you really really really really don’t like math. In both Great Britain and the United States of America, Euclid’s work was once a staple of the classical education, and Euclidean ideas underlay much of how the U.S.A. came together as a nation.
There’s a great scene in the mini-series John Adams (2008) when John Adams (played by Paul Giamatti), Benjamin Franklin (played by Tom Wilkinson), and Thomas Jefferson (played by Stephen Dillane) are working together on Jefferson’s first draft of the Declaration of Independence. Franklin looks at the first sentence of the draft, where Jefferson has written, “We hold these truths to be sacred and undeniable…”, and then suggests that the last phrase “smacks too much of the pulpit.”
Franklin, whose exhaustive reading of course included Euclid, approaches the drafting of this portion of the Declaration in terms of the great Alexandrian’s setting-forth of axioms or common notions that set forth self-evident mathematical truths, and suggests a fateful revision: “We hold these truths to be self-evident…” Jefferson and Adams (themselves both readers and admirers of Euclid’s work) both agree. There is Euclid! – at the very beginnings of the American republic, helping to define terms for a new nation whose existence Euclid never could have imagined.
Similarly, there’s a comparably resonant scene from the Steven Spielberg film Lincoln (2012), where Euclid and his ideas are back at work in American life and history. The film is set at the time in 1865 when President Abraham Lincoln is simultaneously leading the Union cause toward victory in the American Civil War, and guiding the Thirteenth Amendment and the abolition of slavery through the United States Congress. In a thoughtful, understated scene set at the War Department telegraph office, President Lincoln (played by Daniel Day-Lewis) explains to Union Army telegraph operator Samuel Beckwith (played by Adam Driver) how Euclid’s axioms about mathematical equality can be applied to the ideals of human equality for which the Union is fighting:
Euclid's first common notion is this: Things which are equal to the same things are equal to each other. That's a rule of mathematical reasoning and it’s true because it works – has done, and always will do. In his book, Euclid says this is self-evident. You see, there it is – even in that 2,000-year-old book of mechanical law, it is the self-evident truth that things which are equal to the same things are equal to each other.
You don’t have to like math to appreciate Euclid’s Elements – a true classic of world literature. It sets forth eloquently the truth – the self-evident truth! – that numbers don’t lie. It reminds us that, when we solve math problems, we exercise those properties of our minds that will later help us solve problems in life. And it reminds us that the ideas of mathematics have importance and relevance far beyond the math classroom.
I can’t help but think that Mr. Stroot – my 9th-grade geometry teacher at the Catholic prep school I attended in Washington, D.C. – would be pleased to know that I took up an edition of The Elements and read it, from the first axiom to the final solution of the last problem. Q.E.D., Q.E.F.