Transcription
The most effective thinking curriculum in the history of Western civilization is not taught in any MBA program, any law school, or any leadership course. Instead, it's a book written 2,300 years ago called Euclid's Elements. And it has more documented cases of reshaping how great minds think than Oxford and Cambridge combined.
Over my more than 13 years as a peer-reviewed scholar and educator, I've come to believe that Euclid's Elements is the single most under-leveraged intellectual resource available to anyone alive today. And in this video, I'm going to showcase four great thinkers who read this book, the concrete impact it had on them, and show you how it can permanently transform how you think, too.
So, let's start with our first thinker, Abraham Lincoln, because his story is the most concrete illustration of why someone would pick up this geometry textbook and carry it in a saddlebag across Illinois. You see, Lincoln had almost no formal education, a few months of scattered schooling as a child, and then nothing. In fact, he actually taught himself law by reading borrowed books at night. But at some point in his early legal career, he ran into a problem. He was losing arguments he should have been winning, and it wasn't because the facts were against him, but because he didn't know what it meant to actually prove something. He later described this moment of realization. "You can never make a lawyer," he stated, "if you do not understand what demonstrate means." And so, he went home to his father's farm, and he stayed there until he could recite any proposition in the first six books of Euclid from memory. Then he went back to his law practice.
Now, Euclid's Elements is a geometry book, not a law textbook. And so, what was Euclid actually training Lincoln to do? Well, to answer it, we need to spend a moment with the book itself. You see, the Elements opens not with a theorem, but with definitions. A point is that which has no part. A line is a breathless length. A straight line lies evenly with the points on itself. In fact, Euclid defines 23 terms before he begins trying to prove a single thing. And then he does something even more important. He states what are called postulates, which you can think of as his assumptions explicitly. Postulate one, a straight line can be drawn from any point to any other point. Postulate two, a finite straight line can be extended indefinitely. And then he states what he calls his common notions, which are essentially basic logical principles he'll rely on throughout the text. Common notion one, things which are equal to the same thing are also equal to one another.
And so, what makes this all so remarkable? Well, you see, every time Euclid moves from one step in a proof to the next, he cites the rule that justifies the move. In other words, he doesn't just state something like "therefore," but instead something like "therefore by common notion one," or "therefore by proposition four." In other words, nothing in Euclid's Elements is simply asserted. Instead, everything is demonstrated and cited.
And so, what Euclid trained Lincoln to do, and what he trains you to do if you read him, is to refuse to accept any step in an argument that isn't justified by an explicit rule. You see, most people argue by assertion only. They say things like "clearly" or "obviously" or "it follows that" and just move on. Euclid makes that impossible. Every gap has to be closed. Every conclusion has to be earned.
And so, here's an exercise you can engage in from Euclid that is similar to what Lincoln did. The next time you make an argument in a negotiation, a meeting, a piece of writing, whatever, force yourself to write it in three layers. First, define your key terms precisely. What exactly do you mean by success, efficiency, fairness, even risk? Second, state your assumptions explicitly. the things you're taking as given or fundamental without proving them. Third, for every move you make from one claim to the next, name the rule you're applying. If you can't name it, you see, your thinking and understanding probably isn't all that clear.
And so, Lincoln went back to his law practice understanding this kind of discipline. And it's not a coincidence that he became one of the greatest legal minds in American history. But whereas Lincoln came to Euclid through professional necessity, our second thinker here, Thomas Hobbes, came to him by accident. And the story of that encounter is one of the most dramatic intellectual conversion stories on record.
You see, Hobbes was 40 years old, already an educated man, already a scholar by any standard, when he wandered into a library and came across Euclid's Elements open to book one, proposition 47, the famous Pythagorean theorem. From there, he read the conclusion. In a right-angled triangle, the square on the hypotenuse equals the sum of the squares on the other two sides. His immediate reaction, reportedly, was, "By God, this is impossible." So, he read the proof. The proof cited earlier propositions. So, he read those, which cited earlier ones still. And he followed the chain all the way back to the definitions and postulates at the beginning of book one, and realized that everything was airtight. He couldn't find a single gap. The conclusion was not only true, but necessarily true given the axioms. And Hobbes walked out of that library a changed thinker. In fact, his political philosophy, the Leviathan, is structured as a quasi-Euclidean argument. Definitions first, then axioms about human nature, then derived conclusions about what political arrangements necessarily follow from those.
In fact, what Hobbes had stumbled into was Euclid's most powerful technique, what is known in formal logic as the reductio ad absurdum. In book one, proposition six, Euclid proves that if two angles of a triangle are equal, the sides opposite them must be equal, too. But, he doesn't prove this directly. Instead, he assumes the opposite. Suppose the sides were not equal, then one would be larger. You could then construct a smaller triangle inside the original one. But, that smaller triangle would have the same angle sum as the larger one, which contradicts results already proven. Therefore, the sides must be equal. In effect, the assumption of the opposite has destroyed itself. And in book nine, proposition 20, Euclid uses the same technique to prove something that still stops people cold, namely the proposition, there are infinitely many prime numbers. Again, Euclid assumes the opposite. Suppose there are finitely many. Well, list them all. Now, multiply them all together and add one. Well, this new number is either prime, and it's not on your list, contradicting the assumption, or it has a prime factor not on your list, again, contradicting the assumption. Either way, the assumption of finitude becomes impossible.
And so, what reductio ad absurdum trains is something powerful. When you can't prove something directly, simply assume it's false and then follow that assumption wherever it leads. If it leads somewhere impossible, well, you've proven your case. And this doesn't just apply to mathematics. It lies at the heart of effective legal arguments, scientific falsification, and even strategic thinking.
And so, here's an exercise you can engage in with respect to this skill. The next time you believe something is true, but you struggle to demonstrate it, write down its negation, or the opposite claim, at the top of a page. Then follow that opposite claim as far as it will take you. What would have to be true if the opposite were true? And what would that imply? And what would that then imply? Keep following the chain until you either reach a a something that violates what you already know, or until you realize your original belief was shakier than you thought. Both outcomes are valuable. The contradiction gives you a proof, and the failure to find one tells you something important about the limits of what you actually know.
And by the way, if you want to work with me personally on this skill and so many other critical thinking skills that affect the real outcomes in your life, then feel free to check out my Critical Thinking Academy at the link in the pinned comment below. But now that brings us to the third thinker on our list who read Euclid's Elements, Albert Einstein.
Now, Einstein's encounter with Euclid was different from both Lincoln's and Hobbes, and what it gave him was different, too. Einstein was 12 years old when he received what he later called a "holy little geometry book," a copy of Euclid's Elements. And what struck him was not any individual proof, but something about the method as a whole. Here was a system, he thought, where you could start with a handful of simple, self-evident postulates and derive, with complete certainty, from pure thought alone, results that were not at all obvious. The Pythagorean theorem, book one, proposition 47, is again a great example. You see, Euclid doesn't discover it in one move. He builds it. Proposition 47 depends on proposition 41, which depends on proposition 37, which depends on proposition 35, which depends on proposition 14, and so on, all the way back to the first definitions. The entire structure is a dependency chain. No step is possible without the steps that precede it. And the conclusion, that in any right triangle, the areas of the squares on the two shorter sides add up to the area of the square on the longest, emerges from this chain with a kind of inevitability that feels law-like, almost in a physical sense.
And so, Einstein carried this model of thought into physics. For instance, his special relativity begins with two postulates, that the laws of physics are the same in all inertial frames, and that the speed of light is constant for all observers, and derives everything else from them. That method itself is Euclidean. Start simple, be explicit, build carefully, and let the complexity emerge from the structure.
So, here's an exercise you can engage in, inspired by Einstein's reading of Euclid. The next time you face a complex problem, don't try to solve it in one move. Instead, ask what smaller problems you would need to solve first in order for the larger solution to be possible. Build the dependency chain backwards. What must be true for X to work, and what must be true for that to work? Keep going until you reach claims simple enough to verify directly, then build forward from there. And do you see how this isn't just a mathematical habit? In fact, it's the architecture of every sustained complex achievement.
Finally though, we arrive at the fourth and final thinker here, Bertrand Russell. Russell encountered Euclid at 11 years old and later described the experience as "one of the greatest events of my life, as dazzling as first love." You see, Russell had been told by his older brother that they were going to go study geometry together. He was disappointed though to be told that he would have to accept the axioms as given, that Euclid's postulates couldn't be proved, only assumed. He wanted everything to be proven from nothing. But what Russell came to understand, both from reading Euclid and later from his own work in mathematical logic, was that this wasn't a weakness of the system. In fact, it was the system's most important feature. Euclid doesn't hide his assumptions. He states them at the beginning, in plain sight, before a single theorem is attempted. And this is an act of extraordinary intellectual honesty, and it's a habit almost nobody practices in ordinary thinking. Most arguments fail not because the reasoning is bad, but because the assumptions are hidden. In fact, often the person making the argument doesn't know what they're assuming at all. And as a result, the person hearing the argument can't find the assumptions to challenge them. And so, the argument has the appearance of logic while doing the work of assertion, as we've previously seen.
Euclid also shows you in Book 1, Proposition 7, how to rule out impossible configurations, how to prove something by systematically eliminating every alternative arrangement, considering each case and showing that it leads to contradiction. This is what in formal logic is called proof by cases. Instead of asserting something like, "Here's why X is true." you assert, "Here's why everything other than X is impossible." And it's one of the most powerful and least taught reasoning techniques in existence.
So, if we step back and take a look at Lincoln, Hobbes, Einstein, and Russell, what did Euclid actually give them? Because it wasn't really geometry. I mean, none of them actually went on to become geometers. Instead, what Euclid gave them was a model of what rigorous thinking looks like when it's done completely. One, define your terms. Two, state your assumptions. Three, construct rather than assert. Four, cite the rule at every step. Five, break complex problems into simpler ones and solve those first. And six, when you can't prove something directly, assume the opposite and follow it until it destroys itself. And these are far more than simply mathematical skills. Instead, they're cognitive habits.
If you want to keep leveling up your critical thinking to make a massive impact not only on your own life, but also on the lives of countless others, then be sure to watch this next video.