SKEPTICISM ABOUT THE EXTERNAL WORLD- Phil 101 honors Final

Moore's Argument

Moore's Argument 1. Here is one hand. 2. Here is another hand. 3. At least two external objects exist (so an external world exists).

Russell's Partial Reply

The skeptic is correct, a belief's being natural does not mean it is thereby justified. But this is because natural beliefs can come into conflict with one another. The reason the acrophobic is irrational is that he has other natural beliefs which conflict with his belief that his life is in mortal danger whenever he is in high places.

Reid's Basic Idea

There is nothing special about any particular part of one's cognitive nature. It would be irrationally arbitrary to put trust in one part, but not all, of one's cognitive nature.

the Philosophy Sometimes Wins Response

There is reason to doubt that, in situations of conflict, Common Sense always wins out over Philosophy. I.e., there is reason to doubt that (B) is true. A "Common Sense vs. Philosophy" situation is one instance of, or at least very similar to, an "Experience vs. Theory" situation. And in situations of the latter sort,Theorysometimes wins. Example: 2011 neutrinos experiment that made headlines

the Less Simple Response

This response grants the spirit of Russell's Objection, but simply denies that the hypothesis of an ordinary external world is a better explanation of our sense-data than all alternatives, on the grounds that the Evil Demon Hypothesis is a simpler explanation. Since there are different ways of conceiving of simplicity, there are in principle multiple versions of this objection.

External World Skepticism

We are not justified in holding those beliefs about the external world that we hold on the basis of sensory experience. IMPORTANT: This is not just the view that you are not entitled to certainty, rather it's the view that you are not entitled to any degree of belief at all. The basic worry is that we are unable to rule out certain:

the Unanswered Question Retort

What is it rational to do when two or more natural beliefs conflict with each other? Reid's Modified Principle offers no answer (i.e., it says nothing about which natural belief should then be given up). So, by itself, it does not get the result that the acrophobic's belief that his life is in mortal danger whenever he's in high places is the natural belief he should give up (i.e., is the unjustified belief).

Alternative Hypotheses to the Ordinary External World

1. You are dreaming rather than awake. 2. You are being fed your sensory experiences by an evil demon. 3. You are being fed your sensory experiences by an evil scientist who houses your brain in a vat. (≈ the set-up in the movie "The Matrix")

Reid's Modified Principle

A belief is justified if (i) it is a natural belief, and (ii) one does not have positive reason to doubt it in the form of other natural beliefs which conflict with it.

Reid's Principle

A belief is justified if it is a natural belief. (A natural belief will be any belief that either is directly part of our cognitive nature or is the product of other parts of our cognitive nature, such as a faculty of reasoning.) Our sensory experiences, together with the belief that our sensory experiences (at least other things equal) reflect reality, lead us, via some reasoning, to form beliefs about the external world. These beliefs thus arise from our cognitive nature, and Reid's Principle consequently classifies them as justified.

the Natural Vs. Justified Response

A belief's being natural may mean one cannot help but have it, but how does that make it justified? For example, consider someone with acrophobia - the fear of heights. This fear may come naturally to the acrophobic, and may even be unshakable, but we don't think it is thereby justified; we all think the acrophobic is irrational. To put it in terms of beliefs, we could say he has a certain natural belief, namely, that his life is in mortal danger whenever he is in high places; but none of us think this belief is thereby justified.

Russell's Principle

Belief in a hypothesis is justified if it is the best explanation of the relevant data. If successful, Russell's Objection is enough to defeat the Skeptical Argument as it is formulated. But Russell wants do more, he actually wants to show that, in the spirit of his objection, there is positive reason to believe in the existence of an external world as we ordinarily conceive of it:

Russell's Defense of an External World

Belief in the existence of an external world as we ordinarily conceive of it is the best explanation of the sense-data we have. Russell's argument goes by way of his cat example. Suppose you have a bunch of sense-data as of a cat at one time ("cat-shaped" sense-data), and some more sense-data as of a cat at a later time (similarly "cat-shaped"). One possible story is that you simply have such sense-data, and that's it, there's no further rhyme or reason. Each particular sense-datum you have is a brute fact, causally unconnected with all other sense-data you have. But this is not a very good explanation. In particular, to use Russell's term, it is not a very simple explanation, given its lack of order. A better, simpler story is that there actually is a cat that existed at those times when you had those "cat-shaped" sense-data, as well as during the time in between, a cat which is currently responsible for your having the sense-data. This is especially true since, for example, by taking a cat to be hungry, you can explain the particular "behavior" of your "cat-shaped" sense-data. In other words, the hypothesis of an external world as we ordinarily conceive of it allows us to see order in, and so better explain, otherwise disparate phenomena.

a Common Skeptical Theme

Contrary to ordinary thinking, we are not justified in holding a certain belief because we are unable to rule out certain alternative hypotheses on which this belief is in fact false.

the Cognitive Nature Thesis

Our nature simply has a certain constitution, and it's only in virtue of that nature that we are able to think at all. In particular, the constitution of our nature (in the relevant sense) has two aspects: 1. beliefs (mathematical axioms, the future will resemble the past, etc.), 2. belief-forming mechanisms: a. faculties of reasoning (e.g., deductive reasoning), b. non-reasoning capacities, such as a perceptual capacities (e.g., introspection, producing the belief: I'm having a sensory experience as of sitting in a chair right now).

Russell's Objection

Premise 1 of the Skeptical Argument should be rejected. It is not necessary to strictly rule out alternatives in order to be justified in believing a particular hypothesis. It is sufficient to show that this hypothesis is the best explanation as compared to the alternatives when it comes to the data in question. So Russell is in effect appealing to something previously discussed, namely, the Principle of Best Explanation (PBE).

sense-data

Russell uses the term "sense-data" to refer to sensory experiences.

Occam's Version (of the Less Simple Response)

Simplicity is a matter of number of entities (or number of kinds of entities) postulated by the hypothesis. So, since the Evil Demon Hypothesis postulates fewer entities (or fewer kinds of entities) than the hypothesis of an ordinary external world (since it only postulates two, you and the evil demon), it is simpler. (Note that the Evil Demon Hypothesis also sees order in sense-data, given how it sees things fitting together because of the Evil Demon's deception.)

a Contemporary Retort

Simplicity is instead a matter of the length of the description of the hypothesis. And the hypothesis of an ordinary external world is simpler than the Evil Demon Hypothesis in this sense. Let 'EW' abbreviate whatever describes the hypothesis of an ordinary external world. Then the Evil Demon Hypothesis has got to be longer, since it then amounts to: "There is an evil demon deceiving me so that it seems as if EW".

the Internal Conflict Response

The Skeptical Argument does not present a situation in which Philosophy and Common Sense conflict. I.e., (A) is false. A plausible case can be made that premise 1 - the Skeptic's Principle - is itself part of Common Sense, and this is why so many accept it. (What is this plausible case? This is simply Defense #2 from section 2: it seems to be part of ordinary practice that we take ourselves to be justified in believing something only if we have ruled out alternative hypotheses. Recall the example of the hallucinogenic drug.) If this is correct, then what the Skeptical Argument really shows is that Common Sense is in internal conflict(metaphorically, it "self-destructs"), and such internal conflict does nothing to show that we should prefer rejection of premise 1 over acceptance of the conclusion.

Moore's Objection

The conclusion of the Skeptical Argument is so implausible that it is rationally preferable to reject one of the premises rather than to accept that conclusion.

Reid's Objection

The skeptic is being irrationally arbitrary. On the one hand, the skeptic is putting trust in some parts of our cognitive nature: the skeptic grants that we have the sensory experiences we think we do; the skeptic grants that we can identify valid arguments; the skeptic grants that we are correct in thinking validity matters to arguments, etc. On the other hand, the skeptic is telling us not to put trust in another part of our cognitive nature: the skeptic is telling us (in premise 1) not to trust our natural inclination to think that (at least other things equal) our sensory experiences reflect reality. So, we should reject premise 1 of the Skeptical Argument.

Defenses #1 and #2 of premise 1 of the Skeptical Argument

premise 1 Defense #1: If you can't rule out a certain alternative hypothesis, then (as far as your reasons and evidence go) this alternative hypothesis is just as "live an option" as your ordinary belief. So preferencing your ordinary belief would be irrationally arbitrary, and thus you should suspend judgment. Defense #2: The Skeptic's Principle is part of ordinary practice. For example, if you have taken a hallucinogenic drug, you will attempt to rule out a hypothesis of hallucination for any particular thing your senses tell you, and if you can't rule out such a hypothesis, then you won't trust your senses in that particular case. This holds true even now - you won't believe what your senses tell you now unless you can rule out a hypothesis of hallucination. It's just that you will (think you) have ruled out that hypothesis very quickly, either for lack of memory of having taken a hallucinogenic drug, or for the lack of incoherence that is part of the hallucinations of such drugs.

the Skeptical Argument

the Skeptical Argument Suppose someone, X, has a sensory experience as of something, P. 1. Necessarily, X is justified in believing that P on the basis of this sensory experience only if X can rule out all hypotheses (dreaming, evil demon, etc.) other than the one that X is actually perceiving that P. (= the Skeptic's Principle) 2. X cannot rule out all such hypotheses. 3. X is not justified in believing that P on the basis of this sensory experience. This argument is good, no matter who X is and what P is. Thus, generalizing, no one is justified in believing anything about the external world based on his experience. In other words, External World Skepticism is true.