Concepts created during philosophical debates can shape cultures, morality, and even how we do business or wage war. Don’t believe us? Here are five ancient philosophers whose works are still influencing us today.

5. Plato

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You can’t talk about philosophy without including the ancient Greeks. Even the word “philosophy” comes from the Greek word “philosophia,” which translates to “love of wisdom.” Plato is considered by many to be the most famous philosopher of his era. He’s best known as the protege to Socrates (another famous Greek philosopher) and the creator of a series of dialogues that took a deep dive into examining life.

While there’s debate over whether he took too much creative license in drafting Socrates’ conversations in those works, modern philosophers agree that Plato’s works influenced a majority of the philosophical methods and practices that came out of Europe centuries later. In particular, Plato’s Republic is often cited as a political blueprint for creating governments. And in many ways, Plato is credited with being a champion of environmental conservation.

4. Aristotle

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Aristotle studied under Plato, yet the two often saw the world differently. Born to a family of physicians, Aristotle always believed in observation as the key to understanding the world around us. While Plato believed that everyone wanted to be a part of something bigger than themselves, Aristotle countered that people weren’t looking to be part of a movement but rather to find meaning in themselves, through their actions and material things. Many people credit Aristotle as the driving force behind modern-day startups, entrepreneurs, e-commerce, and the internet.

3. Sun Tzu

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If you ask most people to name a Chinese philosopher, they'll probably say Confucius. He was a great thinker, but there’s another man who was equally influential and whose works still shape business and military strategies.

Sun Tzu wasn’t a philosopher in the traditional sense. He was a military general who lived between 544 and 498 B.C.E. However, his experiences on and off the battlefield led to him penning “The Art of War,” a book that outlines the best way to win a literal battle.

Even though the book wasn’t translated into English until the 20th century, modern generals and military strategists credit his concepts as essential learning for anyone preparing for conflict. “The Art of War” is considered required reading at many of the world’s top military academies. But the principles from his work aren’t just relevant for militaries. They’re smart tips for CEOs and entrepreneurs.

2. Niccolo Machiavelli

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In terms of age, Niccolo Machiavelli is the youngest addition to this list. He lived during the Italian Renaissance in Florence and was very active in the political world. Even if you’re not familiar with his name, you’ve heard the saying “Is it better to be feared or loved?” Yes, that was Machiavelli, and the answer was that it’s better to be feared. Machiavelli has a wide list of works, but he’s most well known for his piece “The Prince,” which was penned during his exile from Florence.

“The Prince” is a book that’s often touted as a “must-read” if you’re in business or are thinking of entering politics. Most literary experts agree that the book was written as a response to Machiavelli’s circumstances. He was deeply involved in the political scene in Florence and found himself at the mercy of the Medicis, who didn’t like him. Drama aside, “The Prince” is just as relevant today when it comes to managing enemies, friends, and social climbers, whether in your personal life, business, or politics.

1. Pythagoras

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Pythagoras is the inventor of the Pythagorean theorem (a2 + b2 = c2), an equation that calculates the length for any side of a triangle. So, for that reason alone, he’s still influential.

However, Pythagoras predates Socrates, and in addition to being a mathematician, he was known for being a great thinker. By many standards, until Socrates arrived on the scene, Pythagoras was the most famous and respected philosopher in Greece. However, his mathematical discoveries continue to overshadow other aspects of his life.