Objectivists love to start things out with a big huge, complicated, but simultaneously over-simplified,  pretentious,  irrelevant and really rather silly discussion of the validity of sense perception.  
My brother's book contains a big long lecture on the subject, probably the 100th I have read, always without any original ideas. What normal person goes around lecturing people on the validity of sense perception?

There are several pretend reasons why they do this, and then there is the REAL reason, which is so illogical and so absurd that to put it into words is to destroy it.  But it is something all Objectivists believe implicitly.

I'll leave  that till last.

They really think they are saying something profound.  They claim that the validity of sense perception is the basis of the philosophy of  Objectivism. In fact, a moment's thought will show that the validity of sense perception is not the basis of the philosophy of Objectivism at all, and that it cannot be.

Aristotle said that from two particular propositions no conclusion follows.

Thus, assuming that we can all agree on the following propositions (and I think we can):

a) sense perception is valid
b) the world as perceived through the sense is real and really exists (or: the world exists regardless of consciousness; these are really just 3 or 4 different ways of saying the same thing), then what conclusion follows?

None, as far as I can tell; only that any philosophy that maintains the opposite is untrue.

Thus, these propositions lead nowhere and cannot be the basis of the Objectivist philosophy.

The Irrelevance of the whole discussion

That being the case, why do intelligent people have to waste their time with this kind of thing after 2,000 years?
What would happen if you told Socrates, "When we see a mirage in the desert, it looks real, but we know it isn't, so sense perception is invalid?"
Socrates would say, "How do you know it isn't?"

(In actual fact, a mirage doesn't even look like a lake if you look carefully: a lake doesn't change size and position as you approach it or walk parallel to it.) 

The Aristotelian position is that sense perception is valid, but that your mind can fool you, it's your mind that's at fault. But in practice it comes to much the same thing. If I get killed by a speeding car that I "just didn't see", what difference does it make whether I really saw it? I'm dead. Maybe I "really" saw it but was just too absent-minded to notice, and maybe I didn't, but the practical result is that I didn't see it one way or the other, and I'm dead.

In other words, theoretically, the validity of sense perception is assumed in the very act of denying  it, therefore sense perception is ipso facto valid. The fallacy lies in assuming that the  eye is a camera and that the brain is a computer.

For example, we see what we expect to see, and we find what we're looking for, rather than what's there. Personally, I have a tendency to leave out short words, or to repeat them. When I proofread, I think I see what I think I've written, but it might not be there at all. I've left out a word. I can proofread something 5 times and I'll never see it. Maybe the 6th time.

It seems to me that to a reasonable person, the average person, sense perception is a little bit like memory: it can be very deceptive, but since it's all you've got, you've just got to "stop, look and listen, if you want to stay alive". This is hardly profound.
If you know for a fact that you'll be crushed to death if a freight car moves one foot without warning, you make damn sure you know what's going on at both ends of the train.

What would do you if you had a child who denied the validity of sense perception and the reality of  the world as perceived through the senses?
What are you going to do, stand around arguing philosophy with the little brat?
What do you get whenever you say anything to a philosopher? "No, no, no, we don't say those things at all,  we use those words in a special sense", etc. Two million pages of word-wanking, hair-splitting and jargon for 200 years, that's what you get.

I'll tell you what you'd do, and don't tell me you wouldn't. You'd smack his bottom as hard as you could and say, "THERE'S your proof of the validity of sense perception and the reality of  the external world as perceived through the senses, and you'll get another one twice as hard the next time you say anything else half so stupid. So when you see a car coming you get the hell out of the road, because the car is real, and you'll get killed".

The pretend reason for discussing the validity of sense perception

The pretend reason is to set the Objectivists off from the traditions of the Berkeleians and Kantians, to whom no sensible person (certainly no American) pays any attention anyway, and who don't even believe what they are saying anyway: this is very easy to prove.

For example: put a Kantian behind the wheel of a car. A little girl runs into  the road right in front of him. Does he say "That is only phenomena, we can never know noumena" and run over her and kill her? Or does he get scared as hell and slam on the brakes, with his heart pounding? You know what he'll do. He'll stop the car.  

Put a Berkeleian on a railroad track with a fast train approaching, and let him recite his little mantras all he wants -- "I see the train approaching; I hear the whistle; I feel the road bed vibrating underneath my feet; but where, apart from my perception of these things, is there any proof that the train exists at all?" -- what will he do then? You know perfectly well what he'll do. He'll get out of the way.

What does he say when you call him a faker, hypocrite and liar? The same thing: "OK, you say you saw me step out of the way. But where, apart from your perception of these things, is there any proof that I ever stepped out of the way at all, or that the train or the railroad track ever even existed?"

These people have more tricks than a dog has fleas.

Schopenhauer said, "When you see a building, it only exists in your mind, and if you don't understand that, then you don't understand anything." His solution to the Kantian "thing-in-itself" problem was to say that the "thing-in-itself" only exists in your mind! Yet he slept with 2 loaded pistols on his bedside table every night! He must have believed something was real.

These people are not monsters. They're not crazy. They just doesn't believe what they're saying, that's all. Like many philosophers  and most philosophy students, they are intellectually pretentious, verbally manipulative little attention-seekers dreaming of tenure in some comfortable little college where they can torture and torment students with questions like "prove to me that you exist" at some huge salary.

What is virtually certain is that no one ever saw a speeding car and got killed because he didn't believe it was real.

If these were serious philosophies, these people would have to be institutionalized. They couldn't be trusted to cross the street. But since they are not, why bother answering their arguments?

(Of course, Rand doesn't explain any of this, because she never really explains anything.)

Since that is the case, the whole discussion could easily and profitably be dispensed with. Why bother with it? The Marxists (and just about everybody else) do very for themselves without ever even mentioning all this.

(There: I left out the word "well". Did you notice? I didn't.)

We've just discussed one of the pretend reasons (which are never really explained). Now here comes one of the real reasons:

The real reasons for discussing the validity of sense perception

The first real reason for even mentioning all this is, is simply to establish the whole rarefied atmosphere of intellectual pretentiousness vital to any discussion of philosophy, especially for gullible adolescents (even if they are 50 years old).

The second REAL reason -- in fact, the ONLY real reason of any importance -- the only reason for this whole discussion -- is to brainwash Rand's followers -- and any potential recruits into the vast swarms of Rand's philosophical blind army ants and brain slaves -- with the following non-sequitur:

Reality is objective
Ayn  Rand has perceived reality
Therefore, Ayn Rand is always right.

Didn't you know that? Study Ayn Rand and you'll learn that right away. I'm not exaggerating.

Ayn Rand is infallible. Ayn Rand is omniscient. Ayn Rand is God. Ayn Rand is Moses on Mount Sinai. Ayn Rand is perfection. Ayn Rand is the supreme arbiter of all truth and morality.

Every Objectivist believes these things. You can see this by the way they "solve" complex problems by quoting stupid little slogans like "Man is not a sacrificial animal", or "Racism is the lowest form of collectivism", as if they were really proving something.   

The Objectivists would be far more "rational" (in the sense of "perceiving reality") if they would admit that their philosophy is a religion, exactly like Islam.  The whole question of sense perception is irrelevant.

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