Meditations on First Philosophy

by

René Descartes

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Meditations on First Philosophy: Sixth Meditation Summary & Analysis

Summary
Analysis
The Meditator’s final task is to show that physical objects really exist. So far, his clear and distinct perceptions about God and the imagination suggest that they probably do. But to prove this for sure, the Meditator starts by explaining how imagination is different from pure understanding. If he thinks of a triangle, he imagines a three-sided figure with his mind’s eye. But if he thinks of a chiliagon (a thousand-sided polygon), he doesn’t imagine what it would look like—even though he can understand its geometrical properties. While understanding is part of humans’ essence, the imagination isn’t. Imagination depends on some outside influence. Specifically, understanding involves the mind turning inwards to explore ideas, while imagination involves the mind looking outward to consider unreal physical objects.
Descartes’s fundamental goal in the Meditations is to lay a perfectly reliable, absolutely certain intellectual foundation for science. Thus, his work will not be complete until he can tell scholars what kind of methodology they can use to understand the world around them. In order to do so, he first needs to establish whether people can trust their senses, and whether the things we think we perceive really do exist. He starts with the imagination because it’s entirely in his mind, so he can be absolutely sure that it exists, but it also clearly points to the existence of things that aren’t entirely in the mind.
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Imagination is based on the combination of memory and sense-perception, so analyzing the reliability of the senses is a good place to start. Once upon a time, the Meditator perceived that he had body parts, like limbs and a head, which interacted with other physical objects and felt sensations like pleasure, hunger, and sadness. The body could touch, see, smell, taste, and hear, which allowed it to perceive things like the sky and the ocean—but not thoughts. It also had many strong, involuntary sensations that appeared to come from external objects. The Meditator figured that physical objects resembled his ideas of them, and that sensations like pain and thirst were natural responses to different situations.
In the Second Meditation, the Meditator established that the senses give us an inferior kind of understanding compared to the intellect. Yet this doesn’t mean the senses are irrelevant to true scientific knowledge—on the contrary, they’re actually the only way that scholars and scientists can collect information about the external world so that they can later analyze this information through rationality. Moreover, the Meditator also makes a key distinction here: he is absolutely certain that he has sense perceptions—he cannot possibly doubt that he seems to see, feel, and hear things—but this does not yet mean that the things he perceives are actually real.
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But later in life, the Meditator started to doubt his senses. For instance, he noticed that buildings and statues sometimes looked different from a distance than they did up close. He learned that sometimes amputees still feel pain in the limbs they have lost. At the beginning of these Meditations, he determined that he could not yet prove that he wasn’t dreaming, or that even his clearest perceptions weren’t erroneous.
The Meditator sets up two different levels of skepticism about the senses. On one level, he may be dreaming, in which case none of his sense perceptions are trustworthy. He already has the tools to overcome this kind of skepticism: he already knows that God would not deceive him. But on another level, even if he isn’t dreaming and the external world is totally real, the Meditator still knows that the senses deceive him. Even in perfect conditions, they aren’t reliable enough to lead to certain knowledge. This presents a different challenge: can scientists ever refine the senses’ murky perceptions enough to make them clear and distinct?
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But now, knowledge of God has taught the Meditator to trust in his clear and distinct perceptions. For instance, if he clearly and distinctly perceives two things to be different, then they are. He clearly and distinctly perceives that his essence is to be “a thinking, non-extended thing,” while he has “an extended, non-thinking” body. Thus, he is certain that his mind and body are separate, and that he (the mind) could exist without the body, imagination, and senses. In contrast, imagination and sense-perception can’t exist without the mind: the Meditator needs guidance from his mind to organize his ideas and perceptions.
The Meditator proves that his body must exist by deducing it from an axiom that he has already proven: his clear and distinct perceptions are reliable. Thus, the Meditator reaches a dualist conclusion about human nature: people are the combination of a nonphysical mind with a physical body. But the body and mind are not equal—rather, the mind thinks and controls the body. Effectively, then, the mind is where people’s real essence lies, and the body is just a tool for the mind to use. This model of human nature—often referred to as the “ghost in the machine”— is famously associated with Descartes.
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Yet the human imagination produces ideas and the human senses produce perceptions involuntarily. So what creates them? Either external substances, the Meditator answers, or God. But it can’t be God, because if God made these ideas and perceptions falsely appear to come from physical objects, then He would be a deceiver (and the Meditator already knows that He isn’t). So the Meditator concludes that physical objects exist. They might not be exactly like how we perceive them, but they’re real.
While the Meditator is certain that his body takes up physical space, this doesn’t necessarily mean that all of the other things he perceives exist within this same physical space, too. Rather, he has to prove this separately—as he does in this section. His proof for the existence of physical objects is similar to (but far simpler than) his first proof for the existence of God. Namely, just as he can imagine God only because something with God’s characteristics actually exists, he can only have the impression that there are physical objects because they’re actually there.
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Objects surely have basic mathematical properties like size, shape, and motion. And since God created nature and isn’t a deceiver, it’s likely that human perception about other, more complex properties in objects (like color and sound) also “contains some truth.” Natural sensations like thirst, hunger, and pain suggest that the body has certain needs, and the mind is “very closely joined” to it. Yet other perceptions are clearly unreliable, like the assumption that “space in which nothing is occurring to stimulate my senses must be empty.” So reaching certainty about our perceptions requires putting them up to scrutiny by the intellect.
Having proven that objects are real and our perceptions reflect reality to at least some extent, the Meditator is now ready to lay out basic principles for science. But his ability to do so will depend on whether he manages to sort reliable perceptions (which can form the foundation for scientific knowledge) from unreliable ones (which cannot). This is why he distinguishes between mathematical properties like size, shape, and motion (which are measurable and reliable) and unreliable perceptions, like the assumption that space that appears empty to us actually is empty. Science must be founded on the first kind and steer clear of the second.
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Assuming that perceptions are completely accurate is really “misusing the order of nature.” Perceptions’ purpose is to send the mind general signals about what is good and bad for the individual, but not to provide reliable information about physical objects’ “essential nature.” Perceptual mistakes simply show that humans aren’t omniscient. For instance, when people get sick and eat or drink things that make their sickness worse, this just shows that the natural machinery of their bodies is out of order.
The Meditator uses these examples to illustrate that there’s a significant gap between the way things appear to us and the way they actually are. This point is significant to Descartes because it’s the foundation for the scientific method: science is just a way for humans to rationally test the things that we perceive and determine what their “essential nature” really is. In other words, science helps us turn unreliable perceptions into certain knowledge.
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Next, the Meditator asks how God prevents humanity from deceiving itself. He offers a few observations. First, all physical things can be divided, while the mind never can be. Thus, a person’s mind could be joined to only part of their body—for instance, they could lose limbs but remain the same person. Second, the brain appears to be the only part of the body that has any contact with the mind: it sends signals to the mind about what the body perceives. Third, the different parts of the body are connected and move in consistent ways. For example, foot pain passes through many different nerves to reach the brain, and by stimulating these nerves, we could imitate the feeling of foot pain.
These specific comments about the body might seem out of place in relation to the rest of the Meditations. But actually, they’re just the next logical step: they’re the most clear and distinct observations available to the Meditator about the nature of the human body and the external world. Thus, for Descartes, these principles would be the foundation for a scientific understanding of humankind. Of course, they also reflect the state of medical science in Descartes’s era. For instance, he knew that the brain is central to controlling the body and that the nerves transmit sensation from the body to the brain.
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Fourth, the Meditator says, each movement in the brain produces a corresponding feeling in the mind, and all such natural feelings contribute “to the preservation of the healthy man.” For instance, pain signals to the mind that it should act to eliminate the problem causing the pain. The Meditator concludes that the senses sometimes do deceive—especially when the body is sick and can’t signal sensations to the mind properly. But usually, the senses are truthful, and memory and the intellect can help catch their errors. Thus, the Meditator will generally trust his senses and move on from “the exaggerated doubts of the last few days.”
The Meditator’s claims about the relationship between movements in the brain and feelings in the mind demonstrates Descartes’s specific view of the mind-body connection. Unlike most modern neuroscientists, he doesn’t think that the mind is physically located in the brain—rather, he thinks of the brain as something like the mind’s user interface. He thinks that the mind and body are totally separate, but the brain is the organ in the body that is designed to communicate with the mind. Meanwhile, his claims about the senses point to what he views as the best approach to science: namely, that scholars should use rationality to test and prove the impressions they receive from their senses. This is exactly what scientists do today—they collect data by observing a phenomenon and then logically analyze that data to reach conclusions about it.
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Finally, the Meditator concludes that he can also dismiss his doubt about being asleep. His memory is linking his meditations every day to the day before, and he doesn’t see anything vanishing into thin air, as tends to happen in dreams. He knows that he can trust his memory, intellect, and (for the most part) his senses. He’s confident that God isn’t deceiving him, but he recognizes that humans often make mistakes—and should try their best to avoid them.
At the very end of the Meditations, Descartes’s Meditator comes full circle. He returns to believing that he’s a real person, living in the real world, with senses that give him accurate information about that world. Of course, there’s one crucial difference: he’s now absolutely certain about all of it, because he has gone through the intellectual exercise of identifying and justifying his presuppositions.
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