1. Meditations on First Philosophy
René Descartes

2. Meditations on First Philosophy
René Descartes

3. The Project
Descartes was one of the greatest mathematicians and scientific minds in Western history. He was also a philosopher. As both a scientist and philosopher, what he needed was a firm, secure foundation for his research in science. He needed to know what, if anything, he could be absolutely certain about.

4. The Project
One way to look at it would be this: up to this point, Descartes had never questioned his beliefs. It’s as if he had a built all his new beliefs on a really unsteady foundation, like building a house on a foundation of quicksand.

5. The Project
Instead, he wants to replace that quicksand foundation with concrete: he wants to find a principle of absolute certainty upon which he can build the entire project of science.

6. The Project
So he has to go through all his major beliefs and decide if any of them are certain. It’s a game, of sorts, with important consequences: if he can find something absolutely certain, then science can make sense. If he can’t, then the scientific project is debatable.
Here are the rules he sets out (and we play along at home):
(1) If I can doubt a given belief, no matter how crazy it might be otherwise to doubt it, I must for the moment discount it and eliminate it. If it’s even logically possible to doubt it, no matter how crazy it might seem, it has to go.
(2) For every doubtful belief I discover, I have to eliminate it from my field of experience and see what, if anything, is left.

7. The Project
The metaphor scholars often use is Alice in Wonderland (the Matrix used this, too): we follow Descartes down the rabbit hole into increasingly strange territory to see if anything down there is absolutely, beyond a shadow of a doubt, certain.

8. The Project
To be a little more scientific about it, what Descartes is out to disprove is the position of knowledge skepticism.
The skeptical argument runs as follows and is both sound and valid:
Premise 1: Knowledge requires certainty (if you want to say you “know” something, instead of “I thiiiink that” or “I believe maaaybe that…” you have to be certain)
Premise 2: We can never have certainty (human minds are flawed and fallible; we are error-prone creatures; the history of our claims have been overturned time and again [flat earth; geocentric universe; etc.])
Therefore: We can never...

9. The Project
To be a little more scientific about it, what Descartes is out to disprove is the position of knowledge skepticism.
The skeptical argument runs as follows and is both sound and valid:
Premise 1: Knowledge requires certainty (if you want to say you “know” something, instead of “I thiiiink that” or “I believe maaaybe that…” you have to be certain)
Premise 2: We can never have certainty (human minds are flawed and fallible; we are error-prone creatures; the history of our claims have been overturned time and again [flat earth; geocentric universe; etc.])
Therefore: We can never...have knowledge (we can never know anything)

10. The Project Premise 1: Knowledge requires certainty
Premise 2: We can never have certainty
Therefore: We can never have knowledge

11. The Project Premise 1: Knowledge requires certainty
Premise 2: We can never have certainty
Therefore: We can never have knowledge

12. The Project Premise 1: Knowledge requires certainty
Premise 2: We can never have certainty
Therefore: We can never have knowledge

13. The Project Premise 1: Knowledge requires certainty
Premise 2: We can never have certainty
Therefore: We can never have knowledge

14. Phase 1: The Start
He begins where we must begin: with all the beliefs we currently have about the world:
Beliefs about science
Beliefs about faith
Beliefs about how to treat one another
Beliefs about culture, fashion, art, and value
Etc.
And of all these, we need to see if any are beyond even a shadow of a doubt.

15. Phase 2: The Senses
When he’s thinking about all the billions of beliefs he has about all kinds of things, he notices that most of them come from his senses: things he can hear, smell, taste, touch, and see, are the foundation for a lot of beliefs. So the question becomes: are the senses reliable as a means to acquire beliefs? Or are all those millions of beliefs that come from the senses therefore open to doubt?
“All that up to the present time I have accepted as most true and certain I have learned either from the senses or through the senses; but it is sometimes proved to me that these senses are deceptive, and it is wiser not to trust entirely to anything by which we have once been deceived.”

16. Phase 2: The Senses
But despite the fact that so many of his beliefs come from the senses, he proves that these are not an entirely reliable source of beliefs since the senses can often deceive us. For some examples:
A Mirage

17. Phase 2: The Senses
But despite the fact that so many of his beliefs come from the senses, he proves that these are not an entirely reliable source of beliefs since the senses can often deceive us. For some examples:
Light Refraction
A Mirage

18. Phase 2: The Senses
But despite the fact that so many of his beliefs come from the senses, he proves that these are not an entirely reliable source of beliefs since the senses can often deceive us. For some examples:
Phantom Limb Syndrome
Light Refraction
A Mirage

19. Phase 2: The Senses
Intoxication
But despite the fact that so many of his beliefs come from the senses, he proves that these are not an entirely reliable source of beliefs since the senses can often deceive us. For some examples:
Phantom Limb Syndrome
Light Refraction
A Mirage

20. Phase 2: The Senses
This is enough to demonstrate that most of the beliefs that come from our senses; everything we know because we taste it, smell it, touch it, see it, or hear it, are open to doubt.
But wait! Come onnnnn, says Descartes, what about when there aren’t mirages or light bendiness, or phantom limbs…how about the stuff RIGHT HERE IN FRONT OF MY FACE. Truly I cannot doubt THAT. My senses MUST be reliable at least in cases where there’s stuff right there in front of me, right???
“For example, there is the fact that I am here, seated by the fire, attired in a dressing gown, having this paper in my hands and other similar matters."
Buuuuuuuut....

21. Phase 3: The Dreamscape
There is one occasion in which he can doubt the stuff right in front of his face (i.e., the most obvious and unproblematic information we get from our senses):
“At the same time I must remember that I am a man, and that consequently I am in the habit of sleeping, and in my dreams representing to myself the same things…How often has it happened to me that in the night I dreamt that I found myself in this particular place, that I was dressed and seated near the fire, whilst in reality I was lying undressed in bed! At this moment it does indeed seem to me that it is with eyes awake that I am looking at this paper; that this head which I move is not asleep, that it is deliberately and of set purpose that I extend my hand and perceive it…But in thinking over this I remind myself that on many occasions I have in sleep been deceived by similar illusions, and in dwelling carefully on this reflection I see so manifestly that there are no certain indications by which we may clearly distinguish wakefulness from sleep that I am lost in astonishment. And my astonishment is such that it is almost capable of persuading me that I now dream."

22. Phase 3: The Dreamscape
Thus, the senses seem to fail us no matter what. Whether we’re talking about strange phenomena like mirages, refraction, drunkenness, or whether we’re just talking about “that stuff right here in front of my face,” none of that information is beyond a shadow of a doubt. Therefore, we must discount all beliefs that come from the senses: everything we see, smell, taste, touch, and hear, is now open to doubt.

23. Phase 3: The Dreamscape
So now let’s play along with his second rule; let’s imagine what the world looks like once we discount all beliefs that come from the senses:

24. Phase 3: The Dreamscape
So now let’s play along with his second rule; let’s imagine what the world looks like once we discount all beliefs that come from the senses:

25. Phase 3: The Dreamscape
So now let’s play along with his second rule; let’s imagine what the world looks like once we discount all beliefs that come from the senses:

26. Phase 3: The Dreamscape
So now let’s play along with his second rule; let’s imagine what the world looks like once we discount all beliefs that come from the senses:

27. Phase 3: The Dreamscape
So now let’s play along with his second rule; let’s imagine what the world looks like once we discount all beliefs that come from the senses:

28. Phase 3: The Dreamscape
So now let’s play along with his second rule; let’s imagine what the world looks like once we discount all beliefs that come from the senses:

29. Phase 3: The Dreamscape
So now let’s play along with his second rule; let’s imagine what the world looks like once we discount all beliefs that come from the senses:
...??? ...oh, !

30. Phase 4: ”I think, Therefore…”
Oh man! This sucks!
“I shall consider that the heavens, the earth, colours, figures, sound, and all other external things are nought but illusions and … I shall consider myself as having no hands, no eyes, no flesh, no blood, nor any senses, yet falsely believing myself to possess all these things… I suppose, then, that all the things that I see are false; I persuade myself that nothing has ever existed of all that my fallacious memory represents to me. I consider that I possess no senses; I imagine that body, figure, extension, movement and place are but the fictions of my mind. What, then, can be esteemed as true?”
There is nothing! The skeptic was right! I can be certain of nothing for as I look around in my experiment, I see there is nothing left in all of existence! Nothing that I can be absolutely certain about!
…wait, what? Nothing that I can be absolutely certain about...??

31. Phase 4: ”I think, Therefore…”
…that’s funny...hang on...I already said that I can doubt everything my senses tell me, including the fact that I have a body, so I’m not here any more...if I’m not here anymore, who’s talking right now...who’s still thinking these weird thoughts...?
“I myself, am I not at least something? But I have already denied that I had senses and body. Yet I hesitate, for what follows from that? Am I so dependent on body and senses that I cannot exist without these? But I was persuaded that there was nothing in all the world, that there was no heaven, no earth, that there were no minds, nor any bodies: was I not then likewise persuaded that I did not exist? Not at all; of a surety I myself did exist since I persuaded myself of something.”

32. Phase 4: ”I think, Therefore…”
…that’s funny...hang on...I already said that I can doubt everything my senses tell me, including the fact that I have a body, so I’m not here any more...if I’m not here anymore, who’s talking right now...who’s still thinking these weird thoughts...?
“I myself, am I not at least something? But I have already denied that I had senses and body. Yet I hesitate, for what follows from that? Am I so dependent on body and senses that I cannot exist without these? But I was persuaded that there was nothing in all the world, that there was no heaven, no earth, that there were no minds, nor any bodies: was I not then likewise persuaded that I did not exist? Not at all; of a surety I myself did exist since I persuaded myself of something.”

33. Phase 4: “I think, therefore…”
So now let’s play along with his second rule; let’s imagine what the world looks like once we discount all beliefs that come from the senses:
I doubt everything that exists, including myself!

34. Phase 4: “I think, therefore…”
So now let’s play along with his second rule; let’s imagine what the world looks like once we discount all beliefs that come from the senses:
I doubt everything that exists, including myself!

35. Phase 4: “I think, therefore…”
So now let’s play along with his second rule; let’s imagine what the world looks like once we discount all beliefs that come from the senses:
…? Wait, why am I
still thinking and
doubting and worried
and stuff?

36. Phase 4: “I think, therefore…”
So now let’s play along with his second rule; let’s imagine what the world looks like once we discount all beliefs that come from the senses:
…? Umm…hello?
Why can I still hear
myself...I vanished, right?

37. Phase 4: “I think, therefore…”
“So that after having reflected well and carefully examined all things, we must come to the definite conclusion that this proposition: I am, I exist, is necessarily true each time that I pronounce it, or that I mentally conceive it.”
In other words: I think, therefore I am.
An experiment to clarify this: try to really think about and make the following claim: “I doubt that I exist at all.”

38. Phase 4: “I think, therefore…”
In order to “doubt” that “I” exist, “I” must first exist in order to doubt!
The mind, rather than the senses, Descartes concludes, can give us something absolutely certain.
What are the implications of this?

39. Implications
If we can have a foundation for science, it means we can rebuild science on that firm foundation. Thus science, so long as it’s careful and doesn’t rely on the senses for its ultimate foundation, can give us true knowledge of the world and one another.
But wait, science, medicine, aren’t these all based on using the senses?

40. Implications
By highlighting how the senses can deceive us, Descartes is arguing that we shouldn’t base science on that foundation. We should base it, instead, on the truths delivered to us by the mind alone. That’s not to say we can’t use the senses, it just means we need to be careful on how, precisely, we use them.

41. The Scientific Method
If anyone is interested in going into the sciences or medicine, you’ll be familiar with the general principles of the scientific method. In very general terms, science relies upon:
(1) Repeatability. You need to be able to repeat your experiments, they can’t be random flukes because the laws governing the universe aren’t flukish.
(2) Consensus. Nothing really “counts” in science until someone else can verify and repeat your work. In fact, a lot of people have to do this before it counts as “true.”

42. The Scientific Method
When we think about Descartes’ insights into how the senses can deceive us, we can notice how the senses can still be used, but they must be used carefully:
(1) Repeatability. When the senses deceive us, they tend to do so under specific conditions (heat, rain, darkness, drunkenness, and so on). The same experience conducted twice might yield different results.
(2) Consensus. One person can be mistaken about the information from their senses (colorblind people, for example), two people can be mistaken, ten people can be mistaken, but the entire community will, over time, weed out the mistakes until at last, whatever is left, is most likely the truth.

43. The Scientific Method Repeatability Experiment 1: It’s green
Experiment 3: It’s blue
Experiment 4: It’s green
Experiment 5: It’s green
Experiment 6: It’s green
Experiment 7: It’s green
Experiment 8: It’s green
Experiment 9: It’s green
Experiment 10: It’s green

44. The Scientific Method Consensus Yep! Yep! Experiment 1: It’s green
Experiment 3: It’s blue
Experiment 4: It’s green
Experiment 5: It’s green
Experiment 6: It’s green
Experiment 7: It’s green
Experiment 8: It’s green
Experiment 9: It’s green
Experiment 10: It’s green
Yep!
Yep!
Nope!
Yep!

45. The Scientific Method
Truth and Reality over Time

46. And if there’s time…
The Ghost in the Machine