What did Thomas Nagel intend to distinguish, in distinguishing 'impression' vs 'perception of reality'?

Question

_{Source: pp 15-16, What Does It All Mean? A Very Short Introduction to Philosophy (1987) by Prof. Thomas Nagel}

 According to this view, the idea of a dream from which you can never wake up is not the idea of a dream at all: it is the idea of reality - the real world in which you live. Our idea of the things that exist is just our idea of what we can observe. (This view is sometimes called verificationism.) Sometimes our observations are mistaken, but that means they can be corrected by other observations -- as when you wake up from a dream or discover that what you thought was a snake was just a shadow on the grass. But without some possibility of a correct view of how things are (either yours or someone else's), the thought that your impressions of the world are not true is meaningless.
 If this is right, then the skeptic is kidding himself if he thinks he can imagine that the only thing that exists is his own mind. He is kidding himself, because it couldn't be true that the physical world doesn't really exist, unless somebody could observe that it doesn't exist. And what the skeptic is trying to imagine is precisely that there is no one to observe that or anything else -- except of course the skeptic himself, and all he can observe is the inside of his own mind. So solipsism is meaningless. It tries to subtract the external world from the totality of my impressions; [1.] but it fails, because if the external world is subtracted, they stop being [2.] mere impressions, and become instead [3.] perceptions of reality.

I do not understand 1, because I do not understand how 2 and 3 differ?

Answer 1

Honestly, Nagel's rhetoric is not terribly clear on the distinction of the two terms.

I get the sense that by "impression" he means something vague, not certain, unverified, general; like an impressionist painting is to a photograph; and I think he means something like a memory as well as a "sense impression" (p8) of the case. His comment about "the impression of royalties" also makes me think there is inference at work with his use of "impression". On page 12 he uses "impressions and experiences" as if there are experiences and our impressions of those experiences(impressions of impressions?).

By "perception" he seems to mean what is perceived by the senses and also how it is interpreted. Note that on page 10 he seems to distinguish perception from memory. So perception seems to be more about the immediate experience of the now, and maybe impressions are of the now, but also last into memory?

So... if we [1.] subtract the external world there can be no [2.] "immediate sense impressions turning into memory impressions" and only [3.] mental interpretations constituting reality.

In "What Does It All Mean" Nagel uses "impression" only ten times and "perception" six:

Nagel's uses of "Impression"

Page 8

Whatever you believe — whether it's about the sun, moon, and stars, the house and neighborhood in which you live, history, science, other people, even the existence of your own body - is based on your experiences and thoughts, feelings and sense impressions. That's all you have to go on directly, whether you see the book in your hands, or feel the floor under your feet, or remember that George Washington was the first president of the United States, or that water is H2O. Everything else is farther away from you than your inner experiences and thoughts, and reaches you only through them.

Page 10-11

If you try to argue that there must be an external physical world, because you wouldn't see buildings, people, or stars unless there were things out there that reflected or shed light into your eyes and caused your visual experiences, the reply is obvious: How do you know that? It's just another claim about the external world and your relation to it, and it has to be based on the evidence of your senses. But you can rely on that specific evidence about how visual experiences are caused only if you can already rely in general on the contents of your mind to tell you about the external world. And that is exactly what has been called into question. If you try to prove the reliability of your impressions by appealing to your impressions, you're arguing in a circle and won't get anywhere.

The most radical conclusion to draw from this would be that your mind is the only thing that exists. This view is called solipsism. It is a very lonely view, and not too many people have held it. As you can tell from that remark, I don't hold it myself. If I were a solipsist I probably wouldn't be writing this book, since I wouldn't believe there was anybody else to read it. On the other hand, perhaps I would write it to make my inner life more interesting, by including the impression of the appearance of the book in print, of other people reading it and telling me their reactions, and so forth. I might even get the impression of royalties, if I'm lucky.

Page 12

On the other hand, to conclude that you are the only thing that exists is more than the evidence warrants. You can't know on the basis of what's in your mind that there's no world outside it. Perhaps the right conclusion is the more modest one that you don't know anything beyond your impressions and experiences. There may or may not be an external world, and if there is it may or may not be completely different from how it seems to you — there's no way for you to tell. This view is called skepticism about the external world.

An even stronger form of skepticism is possible. Similar arguments seem to show that you don't know anything even about your own past existence and experiences, since all you have to go on are the present contents of your mind, including memory impressions. If you can't be sure that the world outside your mind exists now, how can you be sure that you yourself existed befare now?

Page 16

...But without some possibility of a correct view of how things are (either yours or someone else's), the thought that your impressions of the world are not true is meaningless.

If this is right, then the skeptic is kidding himself if he thinks he can imagine that the only thing that exists is his own mind. He is kidding himself, because it couldn't be true that the physical world doesn't really exist, unless somebody could observe that it doesn't exist. And what the skeptic is trying to imagine is precisely that there is no one to observe that or anything else — except of course the skeptic himself, and all he can observe is the inside of his own mind. So solipsism is meaningless. It tries to subtract the external world from the totality of my impressions; but it fails, because if the external world is subtracted, they stop being mere impressions, and become instead perceptions of reality.

Nagel's uses of "Perception"

Page 10

But what else is there to depend on? All your evidence about anything has to come through your mind — whether in the form of perception, the testimony of books and other people, or memory — and it is entirely consistent with everything you're aware of that nothing at all exists except the inside of your mind.

Page 14

The skeptic's answer is that the process of scientific reasoning raises the same skeptical problem we have been considering all along: Science is just as vulnerable as perception. How can we know that the world outside our minds corresponds to our ideas of what would be a good theoretical explanation of our observations? If we can't establish the reliability of our sense experiences in relation to the external world, there's no reason to think we can rely on our scientific theories either.

Page 16

So solipsism is meaningless. It tries to subtract the external world from the totality of my impressions; but it fails, because if the external world is subtracted, they stop being mere impressions, and become instead perceptions of reality.

Page 25

If a thing is incapable of movement, it can't give any behavioral evidence of feeling or perception.

Page 28

But there is also a philosophical question about the relation between mind and brain, and it is this: Is your mind something different from your brain, though connected to it, or is it your brain? Are your thoughts, feelings, perceptions, sensations, and wishes things that happen in addition to all the physical processes in your brain, or are they themselves some of those physical processes?

Page 89

The question of survival after death is related to the mind-body problem, which we discussed earlier. If dualism is true, and each person consists of a soul and a body connected together, we can understand how Ufe after death might be possible. The soul would have to be able to exist on its own and have a mental life without the help of the body: then it might leave the body when the body dies, instead of being destroyed. It wouldn't be able to have the kind of mental life of action and sensory perception that depends on being attached to the body (unless it got attached to a new body), but it might have a different sort of inner life, perhaps depending on different causes and influences — direct communication with other souls, for instance.

For a clear use of "perception" and (only one use of "impression"), you might dig this article, "Perceptual Intentionality."

Answer 2

If there were no external world, something outside of the perceiver, then there could be no "mere impressions", since there would be nothing to do the impressing.

Then the only reality would be what the perceiver perceives, which would be perceptions but not impressions.

Answer 3

By 'impressions' he means interpretations of observations, which may be erroneous. By perceptions of reality he means direct knowledge of reality.

A realist understands that impressions are potentially flawed, mediated interpretations of reality (das Ding an sich), which is ultimately unknowable. By contrast, Nagel's solipsist believes his own experience is all that exists so his impressions are the only reality.

Answer 4

Paragraph 1: I think Nagel believes in an objective reality, which he believes can be measured and used to refine your internal perceptions over time. He seems to believe that this is necessary, as otherwise it is meaningless to question your internal perceptions at all.

Paragraph 2: I think Nagel is saying that the physical world must exist, as we are able to question whether it exists. He then extrapolates from this, to state that if the physical world did not exist, then reality would simply be the sum of impressions within your mind, and thus they are no longer impressions, they are reality.

I think he is doing the solipsist argument a disservice here, by jumping to extremes, instead of treating them in a more reasonable manner, as I shall try to explain below:

Paragraph 1: I would argue there may be an objective reality, but that it is impossible for a human to perceive it objectively. This is not necessary, as our survival is due to us making predictions of the outcomes of our actions, and those are based on the history of our perceptions - which are at least consistent enough to enable us to survive until now.

We should question what we think we know, because as we don't objectively know anything, we only have incredibly likely guesses, to live by: I will wake up again if I go to sleep; Eating this food will stop me feeling hungry; Drinking this water will stop me feeling thirsty. It's in our best interests to gain as many alternative perspectives as possible, to ensure we are as close to objective truth as we can get (whilst still accepting there is always a chance we are wrong).

Paragraph 2: I would argue that the physical world does not have to exist for us to question whether it exists, as we may be illusions ourselves, with our thoughts being automated processes that we have no control over. I believe this perspective of his is based on the concept that humans can perceive objective truth, and that our perceptions of our thoughts are objectively certain: ie. we think, therefore we are.

Finally, regarding points [1] [2] and [3], I think in attempting to disprove solipsism, he actually strengthens their argument, as he is basically stating that if you remove the external world from consideration, and base your reality entirely on your impressions of the world (ie. your perspectives), then they stop being impressions and instead become reality itself.

If reality is purely inside your head, this is a valid scenario, and he is correct, that your impressions are your reality. I think because that reality is constantly in flux, he discredits it as a definition of reality - however considering that a human can only ever guess about the outside world, using that which they perceive, his final statement is only bolstering that perception, not discrediting it.

As I write this, I'm realizing that the general definition of solipsism is that the self is all that can be truly known, and sadly I go further than that, into believing that nothing can be truly known, especially not the self, so perhaps my answer only argues from that perspective... I believe Solipsism is as close to my ethos as anything else, however, and that this answer covers it fairly in any case (with this disclaimer at the end).