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6 Major Philosophical Ideas, Explained

Philosophy can be daunting. Over the past two millennia, there have been dozens of movements, doctrines, and various “isms.” The texts can be excruciatingly dense, cryptic, and dry. Yet some philosophical theories are so powerful, they shape the way you think and act without you even noticing. Here are six major philosophical ideas that still resonate today.

1. Plato’s Theory of Forms

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Close your eyes and imagine a perfect circle. Now open your eyes and try to draw one. That’s Plato’s metaphysics in a nutshell: While most of us can conceive of a perfect circle, none of us can recreate one. According to Plato, every object on Earth is imperfect (like the circle you drew) but possesses an ideal “form” (like the perfect circle in your mind). Forms are unchangeable, pure, and ideal. The objects on Earth are mere “shadows” — blemished imitations — of those forms.

While it may sound uselessly abstract, Plato’s Theory of Forms is actually the bedrock of much Western thought. Early Christian writers, for example, adopted Plato’s theory to build their understanding of God and heaven. It was also a major influence on early scientific thought. And it continues to affect our thinking today.

For example, replace the idea of the perfect circle with the perfect justice system. Many people believe that a truly fair, truly ideal system of justice is “out there.” They also believe that the current system falls short of that vision. Our belief that a standard, fixed, and ideal justice system is “out there” as a goal to aim toward is fundamentally Platonic.

This belief that all things possess inherent, discoverable qualities has a name: “Essentialism.” As we’ll later discover, it can be controversial.

2. Descartes’s Dualism

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“I think, therefore I am.” More than a catchy quote, the famous declaration by René Descartes continues to shape the way people live. And it all started in the 17th century when Descartes was engaged in a tit-for-tat on the topic of “radical doubt.”

At the time, many philosophers believed that we learn about certain truths through senses such as touch and sight. Descartes thought that this was wrong: The senses were deceiving. (A person, after all, could be hallucinating or dreaming.) Descartes’ critics responded by asking: “If the senses can be so deceiving, then what’s stopping us from doubting everything, including our own existence?” Descartes’ response: Cogito, ergo sum — “I think, therefore I am.” The fact that you can doubt your own existence, the philosopher said, is proof that you exist.

Mental phenomena, Descartes declared, are not part of the senses. They are not of the physical world at all. Rather, the mind and body are distinct, separate. Consciousness and the mind are not made of physical matter.

This latter argument, called Cartesian dualism, was widely adopted by thinkers across the West and led to a flourishing of scientific thought, particularly in medicine. Writing for the journal Mens Sana Monograph, psychology professor Mathew Gendle notes, “The formal separation of the ‘mind’ from the ‘body’ allowed for religion to concern itself with the noncorpoeal ‘mind,’ while dominion over the ‘body’ was ceded to medical science.”

This advance contributed to great strides in medicine, but it also created problems. For one thing, it encouraged a view that physical and mental problems are entirely separate, without the ability to influence one another. It also promoted a sense that mental experiences are less legitimate than physical ones, contributing to a culture that often stigmatizes mental health concerns. As it turns out, when an entire society separates mind from body, we risk treating mental health problems as less “real,” even though they can affect us just as much as any broken bone.

3. Rousseau’s “General Will”

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Jean Jacques Rousseau never viewed himself as a mere philosopher — he was also a musician, playwright, and composer. But his political philosophy had a more lasting influence than any aria, shaping governments across the world.

In the 1760s, Rousseau was in his 50s and monarchs were still ruling Europe. The Geneva-born thinker believed that kings and queens had no divine right to legislate the masses, however. He outlined these beliefs in a book called The Social Contract, envisioning a world where free and equal people ruled. When the book was promptly banned in France, it proved Rousseau’s central thesis: Individual freedom was easily hampered by the authority of the state.

In The Social Contract, Rousseau spent a lot of time exploring the contradictions of freedom. Society was expanding at the time, and people were growing more dependent on others for survival. A strong state was necessary to help ensure equality and justice. But how could you build strong political institutions — endowed with power and authority — and still protect individual freedoms?

Rousseau’s solution was his theory of “the general will.” Under a monarchy or a dictatorship, laws routinely impinge on freedoms. Rousseau argued that, to protect those freedoms, laws had to be determined by the collective will (or “general will”) of the citizenry. And the best tool to interpret the general will was via democracy. Only then could the state truly serve the will of the people.

Rousseau’s theory is credited with sparking the French Revolution and possibly inspiring many of the Founding Fathers of the United States. Today, many of our political differences continue to revolve around the fundamental tension Rousseau identified: how best to balance personal freedoms with state power.

4. Schopenhauer’s Theory of Aesthetics

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Arthur Schopenhauer was a famous curmudgeon, a wild-haired pessimist who notably helped introduce Western intellectuals to Indian philosophy. His writings, however, would forever change the way we think about art.

Before Schopenhauer, most artwork — whether music or painting or dance — was considered a frivolous diversion or akin to a decorative craft, not an expression of genius or a person’s innermost feelings. But Schopenhauer helped change those attitudes with his theory about the human will. It’s complicated, but briefly: The philosopher believed we are held captive by our wills — our strivings, our desires, our urges — and are doomed to suffer.

One way to escape this suffering, Schopenhauer argued, was through aesthetic experiences. Art functions as a quasi-religious experience, freeing us from the suffering of our own will. Furthermore, he argued, great art was the product not of mere craftsmen, but of genius.

Naturally, a lot of artists liked Schopenhauer’s thoughts on aesthetics. Richard Wagner, Leo Tolstoy, and reams of other creatives trumpeted his work, which elevated art to a higher plane. Thanks to Schopenhauer’s theories, artists and artwork started being lauded as vital and necessary to the health of society. A canon of famous masterpieces was assembled, with people treating their creators with a growing God-like reverence. Many of these attitudes, which helped define 19th-century Romanticism, still persist today.

5. Nietzsche’s Übermensch

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One of the most misunderstood and misappropriated philosophers, Friedrich Nietszche is often cast as a gloomy nihilist. But that gets it wrong. Nietzsche was staring into the headlights of a crisis and wanted to help humanity before it was too late.

In his 1882 book The Gay Science, Nietzsche famously wrote that “God is dead.” But the philosopher wasn’t advocating for atheism, he was making an observation: Christianity had lost much of its power in Europe.

For centuries, Christian thought was — for better and for worse — the foundation of the continent’s value system. But by the late 19th century, science and scholarship had chipped away at people’s faith. Nietzsche saw two possible outcomes: Either people would despair into nihilism and drift away from any moral principles, convinced life had no meaning, or they would try to find new “religions” elsewhere, namely in mass political movements like fascism or communism.

Nietszche shuddered at the thought of the second option, which would later become frighteningly real in his home country of Germany. He argued that people had no choice but to forge ahead through nihilism instead. But rather than embrace a meaningless life — and fall into corrosive despair — he offered a way to overcome this nihilism: the “Übermensch.”

To Nietszche, the Übermensch is a person who rises above the conventional notions of morality and creates new values that embrace the beauty and suffering of existence. Hardly just the stuff of gloomy teenagers, Nietszche’s philosophy aimed to be life-affirming. (In fact, alternate translations of The Gay Science call it “The Joyful Wisdom.”)

6. Sartre’s Existentialism

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Remember Plato’s forms, the idea that everything on Earth is an imitation of an ideal form possessing a distinct essence? Essentialism has helped serve as the foundation of some of humanity’s great ideas. But it’s also been deployed in service of discrimination, suggesting that certain people — based on their race or gender — intrinsically possess specific (often negative) traits.

French philosopher Jean-Paul Sartre thought essentialist thinking was faulty. For Sartre, essences do not pre-exist people. Our world is not an imitation of “forms.” Rather, it’s the reverse: “Existence precedes essence,” Sartre said. Our values, our identity, and our purpose on Earth are not inherent or predetermined. We are not some imperfect manifestation of some perfect cosmic blueprint. Rather, we create our own essence by going out into the word, living, and making choices.

This basic declaration is the very starting point for Sartre’s existentialism, the idea that humans are “condemned to be free” and that “life is nothing until it is lived … the value of it is nothing else but the sense that you choose.”  

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