Problems of knowledge practice questions.

G. E. Moore holds up his hands and says that here is one hand and here is another, concluding that external things exist. What is the standard objection to this reply to the external-world sceptic?

• It begs the question, since the sceptic disputes the very premise Moore claims to know
• It affirms the consequent, since it infers a conditional's antecedent from its consequent
• It attacks the person, since it treats the sceptic's doubt as mere bad manners
• It equivocates on 'know', since the word changes sense between premise and conclusion

Answer: It begs the question, since the sceptic disputes the very premise Moore claims to know

Moore's premises may be more certain to him than any premise the sceptic can offer, but the sceptic denies exactly what the proof assumes, so the argument is valid without being able to move the opponent. The objection concerns what the proof can accomplish in the dispute, not whether Moore's claim is true.

A stick half submerged in water looks bent, although nothing about the stick has changed. The argument from illusion uses such cases to conclude that

• physical objects change their properties when they are placed in water
• what we are immediately aware of is not the physical object itself
• perception never gives us any information about the world at all
• the senses are perfectly reliable once an observer corrects for the medium

Answer: what we are immediately aware of is not the physical object itself

The argument moves from a mismatch between how the object is and what is presented to the postulation of an intermediate object of awareness, the sense-datum, and hence to indirect realism. Direct realists block the second step, treating looking bent as a way the stick appears rather than as a further object.

A student argues: different cultures accept different claims as knowledge, so no claim about what is justified holds independently of a culture's standards. What is the standard logical objection to this move?

• It affirms the consequent, inferring the antecedent from the consequent
• It attacks the person advancing the rival view instead of the argument itself
• It draws a normative conclusion from a purely descriptive premise
• It presents two options as exhaustive when further alternatives are available

Answer: It draws a normative conclusion from a purely descriptive premise

That different groups accept different things is an anthropological observation, whereas the claim that none of them is better justified is an epistemic verdict, and the second does not follow without a further premise. The gap has the same shape as the is-ought move Hume identifies in moral reasoning.

A sceptical argument runs: you do not know that you are not a brain in a vat; if you knew you had hands you would know you were not a brain in a vat; therefore you do not know that you have hands. The principle that the argument needs in its second premise is that

• a belief counts as knowledge only if it was formed by a reliable process of belief formation
• every proposition that is possible to doubt must be doubted before inquiry can begin
• knowledge extends to what one knows to be entailed by what one knows
• perception is a less secure source of belief than reasoning from self-evident premises

Answer: knowledge extends to what one knows to be entailed by what one knows

That principle is closure, and identifying it is what makes the argument answerable: one may reject the first premise, as Moore in effect does, or reject closure, as Nozick does. Without naming the principle the argument looks like brute intuition.

Arnauld objects that Descartes uses clear and distinct perception to prove that God exists and is no deceiver, and then uses God's non-deception to guarantee that clear and distinct perception is reliable. The objection is that the argument

• moves in a circle, since each of the two claims is used to support the other
• relies on a premise about God that Descartes' contemporaries would have rejected
• appeals to sense perception at a point where the method of doubt has excluded it
• assumes that an evil demon is possible, which the argument later needs to deny

Answer: moves in a circle, since each of the two claims is used to support the other

The standard reply on Descartes' behalf distinguishes what is clearly perceived at the moment of perceiving from what is remembered as having been clearly perceived: the divine guarantee is needed only for the second. Whether that repairs the argument is one of the enduring disputes about the Meditations.

Chisholm sets out a difficulty he calls the problem of the criterion: to identify which of our beliefs are knowledge we need a criterion, and to establish a criterion we need to know which beliefs are knowledge. Someone who breaks into this circle by beginning from particular cases that she takes herself to know, and derives a criterion from them, is adopting

• methodism, since she begins from a general standard and applies it to cases
• scepticism, since she concedes that neither the cases nor the criterion can be settled
• particularism, since she treats certain instances of knowledge as her starting point
• relativism, since she allows that different communities may start from different cases

Answer: particularism, since she treats certain instances of knowledge as her starting point

The two entry points give the two positions, and each has a cost: the methodist risks a criterion that condemns most of what we take ourselves to know, while the particularist assumes at the outset what the sceptic disputes. The problem is that no third, neutral starting point is available.