If you still have Cartesian-style doubts about how the physical could interact with the mental, then I suggest you buy a physical bottle of scotch, pour it down your physical throat, and wait to see if any mental changes take place.
—  Philosophy of Mind professor
Will the sun rise in the east tomorrow?
  • Hume:The sun has risen in the east everyday in the past, but there is no way to know for sure that it will rise in the east tomorrow
  • Descartes:The sun might not be real, tomorrow might not be real. I am real. God is real. That's it.
  • Kant:You will probably perceive the sun as rising in the east tomorrow because that is what your preset knowledge tells you will happen, but "tomorrow" and "the east" are concepts that don't exist without human perception.
  • Hobbes:Who cares? People suck.
How do you know you exist?

But, really. How do you know you’re real?

In his ‘Meditations on First Philosophy’, René Descartes tried to answer that very question, demolishing all of his preconceived notions and opinions to begin again from the foundations.

Sure, you have your senses. But your senses often deceive you. Maybe the body you perceive yourself to have isn’t really there. Maybe all of reality, even its abstract concepts like time, shape, color, and numbers are false.

And, who’s to say you’re not dreaming? When you’re awake, you know you’re awake. But, when you’re not, do you know you’re not? How do we know that this right here is not a dream? What if you’ve been tricked into believing that reality is real? The world, your perceptions of it, your very body - you can’t disprove that they’re all just made up. And how could you exist without them? You couldn’t, so - you don’t.

Life is but a dream, and I bet you aren’t row-row-rowing the boat merrily at all. You’re rowing it wearily. Like the duped, non-existent doof you are/aren’t. 

Don’t buy it? Good. Have you been persuaded? Even better. Because by being persuaded, you would prove that you are a persuaded being. You can’t be nothing if you think you’re something, even if that something…is nothing. Because no matter what you think, you’re a thinking thing.

Or, as Descartes put it, “I think, therefore I am.”

And so are you. Really.

From the TED-Ed Lesson How do you know you exist? - James Zucker

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