0:00:07.693,0:00:10.063
How do you know you're real?

0:00:10.087,0:00:12.932
It's an obvious question[br]until you try to answer it,

0:00:12.956,0:00:14.661
but let's take it seriously.

0:00:14.685,0:00:17.135
How do you really know you exist?

0:00:17.159,0:00:19.849
In his "Meditations on First Philosophy,"

0:00:19.873,0:00:23.018
René Descartes tried to answer[br]that very question,

0:00:23.042,0:00:26.148
demolishing all his preconceived[br]notions and opinions

0:00:26.172,0:00:28.963
to begin again from the foundations.

0:00:28.987,0:00:32.272
All his knowledge had come[br]from his sensory perceptions of the world.

0:00:32.296,0:00:33.645
Same as you, right?

0:00:33.669,0:00:37.400
You know you're watching this video[br]with your eyes, hearing it with your ears.

0:00:37.424,0:00:40.275
Your senses show you the world as it is.

0:00:40.299,0:00:43.165
They aren't deceiving you,[br]but sometimes they do.

0:00:43.189,0:00:46.032
You might mistake a person[br]far away for someone else,

0:00:46.056,0:00:48.449
or you're sure you're about[br]to catch a flyball,

0:00:48.473,0:00:50.649
and it hits the ground in front of you.

0:00:50.673,0:00:52.501
But come on, right here and now,

0:00:52.525,0:00:54.766
you know what's right[br]in front of you is real.

0:00:54.790,0:00:57.364
Your eyes, your hands,[br]your body: that's you.

0:00:57.388,0:01:00.837
Only crazy people would deny that,[br]and you know you're not crazy.

0:01:00.861,0:01:03.339
Anyone who'd doubt that must be dreaming.

0:01:03.363,0:01:06.376
Oh no, what if you're dreaming?

0:01:06.400,0:01:08.084
Dreams feel real.

0:01:08.108,0:01:10.067
You can believe you're swimming, flying

0:01:10.091,0:01:12.553
or fighting off monsters[br]with your bare hands,

0:01:12.577,0:01:15.029
when your real body is lying in bed.

0:01:15.053,0:01:16.068
No, no, no.

0:01:16.092,0:01:18.406
When you're awake, you know you're awake.

0:01:18.430,0:01:21.761
Ah! But when you aren't,[br]you don't know you aren't,

0:01:21.785,0:01:24.962
so you can't prove you aren't dreaming.

0:01:24.986,0:01:29.025
Maybe the body you perceive[br]yourself to have isn't really there.

0:01:29.049,0:01:31.970
Maybe all of reality,[br]even its abstract concepts,

0:01:31.994,0:01:36.434
like time, shape, color[br]and number are false,

0:01:36.458,0:01:38.288
all just deceptions concocted

0:01:38.312,0:01:40.267
by an evil genius!

0:01:40.291,0:01:41.957
No, seriously.

0:01:41.981,0:01:46.870
Descartes asks if you can disprove[br]the idea that an evil genius demon

0:01:46.894,0:01:49.721
has tricked you into[br]believing reality is real.

0:01:50.580,0:01:53.969
Perhaps this diabolical[br]deceiver has duped you.

0:01:53.993,0:01:56.769
The world, your perceptions[br]of it, your very body.

0:01:56.793,0:01:59.696
You can't disprove[br]that they're all just made up,

0:01:59.720,0:02:01.820
and how could you exist without them?

0:02:01.844,0:02:03.830
You couldn't! So, you don't.

0:02:03.854,0:02:05.819
Life is but a dream,

0:02:05.843,0:02:10.270
and I bet you aren't row, row,[br]rowing the boat merrily at all, are you?

0:02:10.294,0:02:11.939
No, you're rowing it wearily

0:02:11.963,0:02:17.205
like the duped, nonexistent[br]doof you are/aren't.

0:02:17.229,0:02:18.778
Do you find that convincing?

0:02:18.802,0:02:20.049
Are you persuaded?

0:02:20.073,0:02:23.236
If you aren't, good;[br]if you are, even better,

0:02:23.260,0:02:25.205
because by being persuaded,

0:02:25.229,0:02:28.283
you would prove[br]that you're a persuaded being.

0:02:29.132,0:02:31.749
You can't be nothing[br]if you think you're something,

0:02:31.773,0:02:34.171
even if you think[br]that something is nothing

0:02:34.195,0:02:37.590
because no matter what you think,[br]you're a thinking thing,

0:02:37.614,0:02:42.305
or as Descartes put it,[br]"I think, therefore I am,"

0:02:42.329,0:02:43.781
and so are you, really.

0:02:43.805,0:02:44.938
(Airplane engine)