Eli5: What does ‘I think therefore I am’ mean and why is it a big deal?

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Eli5: What does ‘I think therefore I am’ mean and why is it a big deal?

In: Culture
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Descartes (the man who wrote it) wanted to find something that’s objectively true

You can’t trust your senses since they wrong you a lot, mathematics could be different, etc.

At the end of his long experiment, he took a step back and notice that something (that thinks) did an experiment and that’s true.

It’s probably the only thing you can prove and only to yourself.

The phrase “I think therefore I am”, or “Cogito ergo sum” in Latin, was made popular by the philosopher Rene Descartes.

In his work, he goes about destroying the assumptions that most people had in philosophy before him. Many people would say, “ah well I see the sun, or I feel the grass, so therefore it exists”. Descartes basically said, “ok, but what if your brain is in a jar, and you are just dreaming all of this?”

Philosophy is based on axioms. Axioms are self-evident facets of reason that allow you to construct the rest of philosophy on them. Descartes basically argued that all of the axioms that had previously been used were wrong because they were not self-evident. In the same sense that you don’t know you are in a dream when you are dreaming, how do you know that anything around you is as it truly is? So he started his philosophy with doubting **everything.**

At first, he couldn’t figure out where to go from there. How are you supposed to know anything if you doubt everything? Eventually, he discovers his first axiom: I think therefore I am. In order for him to doubt everything, **he** must exist. He can’t assume anything about who or what he really is but he can safely assume that he exists, otherwise, he would not be thinking about the fact that he exists.

Try this experiment. Imagine yourself as a body without a consciousness. It’s very difficult or even impossible to really do. Now imagine yourself as a consciousness without a body. Not that difficult to imagine.

Back in the olden days, there were lots of things people thought were true but hadn’t properly thought about. Then this guy, Des, decided to try to work out what was true and what wasn’t. He started by looking at science, and realised he couldn’t prove any of it. Then he looked at what he could see, and realised his brain might be being tricked by magic. In the end, he decided the only thing he knew for sure was that he was thinking about this stuff, and if he was thinking then he must exist!

From then on, he started to get people to think differently. Everyone started to try to work out what was real, and what wasn’t. In the end, many things people thought were true were nonsense, and many things people didn’t know before were discovered!

I hope I have explained that in a way a 5 year old might understand. For explanations for higher age groups, please see other comments, including that from xPanZi.

Has your brain ever lied to you? It probably has; between sensory illusions, deja vu, hallucinations, dreams, false memories, etc., our perception of what is real is very suspect; your mind plays tricks on you. Descartes basically said that the only thing you can know with any real certainty is that you exist, and you know that because you are the one thinking about existing.

The philosopher Descartes wanted to find a fact that was always 100% true no matter what situation. (This is called an objective truth)

Since the brain constantly misinterprets sensory information (eg optical illusions), Descartes concluded that nothing a person senses can be objectively true, everything could possibly be a hallucination and not real at all.

The one objective truth he found was that no matter what his conscious definitely exists, because if it didn’t then obviously Descartes couldn’t be thinking anything at all.

Hence the phrase “I think, therefore I am.” – Even though you can’t be certain anything physically exists, you know your conscious exists in one form or another because you’re able to make thoughts in the first place.

Here’s how it was explained to me, long long ago:

Imagine you’re just a brain in a jar, and aliens have hooked you up to a machine that creates a fake world for you to live in. Everything you know, or have ever known, has been fake. All of the people have just been simulations, all of the History is fiction. How do you know that you’re not fake, too? Well, you’re capable of thinking. And that’s how you know that you’re real and not just another simulation.

Logically, there are two cases – “I” either exist, or “I” don’t.

If I exist, that’s fine.

If I am being fooled into thinking I exist, that means I must exist in order to be fooled!

Many people here are getting this wrong. Descartes reasoned (due to the many philosophical upheavals at the time) that many of our fundamental beliefs are in question, and desired to start from scratch to see what he could absolutely determine as true.

He decided start by doubting everything, even his own existence. But he reasoned that doubting is an act of thought, and that something that doesn’t exist cannot think. Thus the reasoning: “I doubt therefore I think, I think therefore I am”.

The problem is that this argument only demonstrates ones own existence. I can use it to demonstrate to myself that I exist, but I cannot use it to demonstrate to you that I exist (and visa versa). This is known as the problem of “Hard Solipsism”, and can essentially be summed up as the idea that you can’t actually prove you aren’t in a simulation (like the matrix), as all external stimuli (everything your five senses tell you) could potentially be false data fed to you by the simulation.

Reminds me of my favourite professor’s worst joke:

Rene Descartes walks into a bar. A man asks him if he would like to dance. Rene says “I think not,” and disappears.

are you a computer simulation? are you inside a dream of someone else? are you real??

well, I’m thinking of it, so I must actually exist