Posts Chapter 13 Skepticism I: The Quest for Certainty

Chapter 13 Skepticism I: The Quest for Certainty

Skepticism is basically against the common sense view that I believe many facts about the external world, myself, the past, scientific knowledge and general moral truths.

The Possibility of Pervasive Error

Despite vividly seeing a green field, that cannot help believing I do, but I could be hallucinating. And what I believe really isn’t there.

Perfectly Realistic Hallucination

I do not believe I am hallucinating. I might find that to be an impossibility provided the hallucination is vivid and steady as my present visual experience. When it comes to justification, I’m justified in believing what I perceive, but this is a false comfort if I’m having a vivid hallucination.

At this point, I can be aware that hallucination is a possibility. If I’m aware of this, can I be justified in believing there is a green field before me?

Two Competing Epistemic Ideals: Believing Truth and Avoiding Falsehood Both of these ideals are what one wants to achieve, but they pull against each other. Perceiving inclines us to believe readily, but I may suspend judgment, so I don’t believe a falsehood.

Former: Calling on us to believe truths - believing on grounds that are evidentially too thin or without grounds. Thereby believe too much. Latter: Calling on us to avoid believing falsehoods - believing only on conclusive grounds thereby believing too little.

How does one believe the two? The easiest way is to just suspend judgment. This kind of response is characteristic of Pyrrhonian Skepticism. In broad terms, skepticism is most commonly conceived by philosophers roughly as the view that there is little, if any, knowledge. This is known as knowledge skepticism.

A related kind of skepticism is a feature of temperament, such as believing without conclusive grounds. Skepticism may also target justification. Justification skepticism is the view that we have little, if any, justification for belief.

Some Dimensions & Varieties of Skepticism

Much skepticism is restricted to a given subject, for instance to propositions about the world outside of oneself, or about the past/future, or ethics/religion, science. There is also differences in the status of knowledge and degree of justification.

First order skepticism: it concerns sorts of beliefs or knowledge typical of the kinds grounded in experience or reason, such as beliefs about ordinary perceptual beliefs. Second order skepticism: would say if I know this, I do not know that I know this.

A first order skeptic is committed to second order skepticism. A second order skeptic may believe in first order knowledge, but no one knows this.

Skepticism Generalized

The skeptical challenges brought forward can be directed against all our beliefs about the external world, all our memory beliefs, beliefs of the future, all beliefs about any subject, provided they depend on memory. Memory is at least as liable to error as vision.

Skepticism About Direct Knowledge and Justification

Skeptics hold that since our sense can be deceived by say hallucination, this prevents beliefs generated by senses as being justified - and precludes them from being justified. Another type to consider is memorial hallucination, which could be a memory that is more of a fantasy then a real memory.

Skeptics hold that same view when it comes to the a priori or like math. Why? Because memory is involved. You could misremember propositions or have a memorial hallucination.

Inferential Knowledge and Justification: The Problem of Induction

There are some difficulty that our basic sources can be transmitted inductively. This was mainly brought up by David Hume on how to justify inductive inferences. Basically he said you can’t know true premises inductively reasoned lead to a true conclusion.

Example: The sun has always risen in the east, therefore tomorrow it will rise in the east. Hume would argue that one can’t know that this will definitely happen.

The problem of Other Minds

Since we have no access to the minds of others, how do we know there are other minds? Are we just seeing bodies controlled by a puppet master or machines? Can we even be justified in believe there are other minds? It may be argued that inference to the best explanation is self-evident.

Moderate abductive principle: if our only good explanation for a proposition we are amply justified in believing entails the truth or likely truth of a further proposition, we are prima facie justified in believing the latter proposition. Skeptics deny this because they question whether the adductive principle is self-evident or even true.

The Egocentric Predicament

A position that makes it seem clear that all we can (empirically) know about the world concerns our own present experience. Perhaps I’m a lone conscious ego vividly hallucinating a non-existent physical world. This view of only oneself is called solipsism.


Three Kinds of Infallibility

Is there really any reason to doubt introspectively grounded beliefs constitute knowledge? The skeptical argument is based on the infallibility claim about knowledge. If you know, you cannot be wrong. If adding the premise that you can be wrong in holding a given introspective belief, it would follow this belief does not represent knowledge. This argument from fallibility can be applied to just about every sort of proposition.

We find that the infallibility claim is ambiguous. It could mean three different things.

\1. It must be the case that if you know that is something true, then it is true (ie: you can’t know something that is false). Call (1) the verity principle since knowledge must be truths. Knowledge can never have a falsehood as its object. 2. If you know that something is true, then it must be true - the proposition you know is necessarily true (ie: you can know only necessary truths). Call (2) the necessity principle - knowledge is of necessary truths. Knowledge never has among its objects any proposition that could possibly fail to hold. 3. If you know that something is true, then your belief of it must be true, in the sense that you believing it entails or guarantees its truth (ie: only beliefs that cannot be false constitute knowledge). Call (3) the infallibility principle proper - only infallible beliefs constitute knowledge. It connects with skepticism more closely than (1) or (2). Knowledge is never constituted by fallible beliefs, those that can have falsehoods among their objects.

Knowledge and Fallibility

We can now assess the skeptical reasoning that employs the infallibility claim (in one way or another).

\1. The verity principle - is plainly true. In this sense, knowledge is infallible, but it provides no reason to conclude that I do not know that I’m thinking. The verity principle is itself a verity, but it does not advance the skeptical cause. 2. The necessity principle - seems mistaken. Even if it were true, a skeptic could not reasonably use it - without first defending it by adequate argument against the common sense view or perceptual beliefs. 3. The infallibility principle - seems to give the skeptic an argument against common sense - is the way skepticism can trade on the ambiguity of the formulation.


Uncertainty leaves us with little (or no) knowledge. If I have a vivd hallucination, can I ever be certain that I know I’m seeing what I perceive?

Knowing, Knowing for Certain, and Telling for Certain

In chapter 10, it was argued that knowing doesn’t imply knowing for certain. Skeptics may still maintain that the certainty principle undermines the common sense view that we have perceptual knowledge.

Entitlement as a Requirement for Inferential Justification

The backup principle depends on the assumption that in order to know that something is true, one must have grounds that entails its truth. The common sense view rejects this assumption.

Knowing and Showing

‘Do you know?’ Tends to move discussion to a second order context - grounds for the second order proposition. The show-know principle being able to show something one believes, even being able to prove it, entails knowing it.

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