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Epistemology is the branch of philosophy that deals with the theory of knowledge.

Scepticism - the view that human beings either do not or cannot attain knowledge.

With respect to many of our beliefs we enjoy what has been called 'practical certainty'.

But philosophers ask whether another kind of certainty is possible - call it 'theoretical' or 'metaphysical' certainty.

Is the confidence about the truth of a belief ever fully justified?

Practical success does not guarantee the truth of any particular belief.

Our beliefs form a system that functions as a model of reality. We generally trust the model because it works.

This appeal to practical success only proves the model's usefulness; it does not prove its truth.

Descartes's methodological doubt

The most famous attempt to tackle this problem to refute scepticism by showing we can be absolutely certain about some things, was made by the French philosopher Rene Descartes (1596 - 1650).

In the early 17th century, the new science pioneered by people like Copernicus, Bacon and Galileo encouraged people to challenge accepted authorities and traditional ways of thinking.

Scholastic theologians felt threatened by this new outlook, and defensively turned towards scepticism.

Descartes carried this to the extreme, embracing 'methodological scepticism' - consisting in adopting the most radically sceptical attitude possible, to see if there are any beliefs impervious to doubt.

'I think, therefore I am' - this, he claims, is an indubitable certainty that can serve as his philosophical foundation and lay to rest the spectre of scepticism.


Syllogism - a logical argument with premises and a conclusion:

Premise 1: Whatever thinks, exists
Premise 2: I think
Conclusion: I exist

Our beliefs about our own subjective states are indubitable, and these beliefs constitute knowledge. However, this is hardly a complete or satisfactory victory over scepticism.

Most of what we think of as knowledge concerns not our subjective states, but the way things are in the objective world.

What is noteworthy about Descartes's approach is that he tries to lay the foundations of all philosophical and scientific knowledge entirely by a priori reasoning (that is, by reasoning that does not appeal to sense-experience or observation).

Rationalism - the view that we can establish important truths about the world by reason alone, unaided by sense experience. This is contrasted to:

Empiricism: the view that all knowledge of the world rests on sense-experience.

Note: Rationalists like Descartes never deny the need for empirical study; and empiricists like John Locke (1632 - 1704) usually recognise that some fundamental principles, as well as mathematics and logic, are not based on mere generalisations from experience.

Kant is sometimes credited with reconciling rationalism and empiricism.

He argued that our experience of the world is shaped in some ways by our minds; this allows us to have some a priori knowledge, and to this extent the rationalists were correct. However, he also insisted that this a priori knowledge is always about the spatio-temporal world we experience; it never goes beyond it. In this respect the empiricists were right.

Direct realism - the belief that our senses put us in immediate contact with the physical world. It has 2 appealing features:

1/ It accords with common sense
2/ It denies a foothold to sceptical doubts about the match between our subjective experiences and objective reality

Direct realism has to be rejected for the reasons below:

- A good theory should be able to EXPLAIN common sense
- If veridical sense-perceptions are intrinsically indistinguishable from hallucinations, then I cannot be in unmediated contact with physical reality in either case
- There is a difference between the subjective claim that I am having certain sense-experiences and the objective claim that a material objects exists independently of these experiences.
- It is possible for me to have a sense-impression of something that no longer exists (looking at a distant star)


Representative theory of perception - an account of cognition which holds that what we actually perceive are our own subjective sense impressions, from which we make inferences about the existence and nature of things in the material world.

Representative realism: the view that our sense impressions are caused by the properties of independently existing physical entities, and that we can infer things about these entities on the basis of our impressions. It does not hold that we are in direct perceptual contact with these independently existing things.

It is not such an easy matter to prove the reality of a world that exists beyond my subjective experiences and gives rise to them. The natural first move is to appeal to sense-experience. On reflection, it is hard to see how any sense-experience can suffice. According to the representative theory of perception, I am never in direct contact with independent existing reality. I perceive only my sense-data. Material objects are posited in order to explain why I have the sense-experiences I do. But between me and them is always a VEIL OF PERCEPTION. I can never apprehend the world except behind this veil.

Berkeley's idealism:

Idealism: the view that reality is essentially mental

In Berkeley's view we should take a harder look at what we think an object is. Why not entertain the idea that an object is nothing over and above our perception of it.

To all intents and purposes, an apple is nothing over and above a collection of sensible properties.

George Berkeley (1685 - 1753)

Throughout his life his guiding intellectual purpose was to defend religion from what he saw as the threat posed by the materialism of the new sciences which, in his view, encouraged scepticism and atheism.

In his book Principles of Human Knowledge, he attacks various aspects of the 'representative realism' of Descartes and Locke - in particular the doctrine that our sensations are caused by material substances existing independently of us in space.

On Berkeley's view the whole idea that objective reality is material and exists independently of any perceiving subject is mistaken. Objects can only exist in the mind.


Berkeley's philosophy is very simple. He argues that:

- representative realism and the representative theory of perception are untenable
- objects cannot exist without being perceived
- objects continue to exist even when I am not perceiving them

We are forced to conclude that objects must be perceived by some other mind when I am not perceiving them. He identifies this other mind with God. What we call things or objects are ideas in God's mind. The cause of our sensations is God himself.

The basic problem Berkeley identifies is that if we posit imperceptible causes of our sensations that exist independently of us, then we are abandoning a true empiricism. Instead of restricting our knowledge claims to the world of possible experience, we are indulging in a form of speculation that lacks a philosophical justification, even though it may accord with common sense.

Convinced by this, a number of thinkers have adopted a position known as phenomenalism.

Phenomenalism - the view that all claims about the world must be understood solely in terms of our actual and possible sense-experiences.

Whereas Berkeley said 'to be is to be perceived', which makes objects mind dependent, his phenomenalist successor John Stuart Mill described objects as 'permanent possibilities of sensation'. This definition of an object aims to maintain a rigorous empiricism, refusing to talk about anything that lies beyond possible experience.

Several objections to phenomenalism:

1/ What is responsible for our sensations? There must be a reason

2/ Impressions received by the different senses are coherent. What explains this?

3/ Is it possible to posit other people's minds?

It seems to be a slippery slope leading to the view that the world consists entirely of my own mind and its contents.

Solipsism - the view that nothing exists except one's own mind and its contents.

Almost any form of realism conceives of knowledge as involving beliefs that are true because they correspond to an independent existing reality. But this notion of an independently existing reality is philosophically suspect.


Cognitive relativism - the view that the truth or falsity of a statement is always relative to the theoretical framework of some particular community. No standpoint can be proved to be superior to all others.

Relativism is a view that is more commonly held about moral values than about truth.

The main criticism of relativism is:

How can they deny any standpoint is privileged and yet, by adopting one rather than another, implicitly affirm its superiority?

In essence, the criticism is that relativists necessarily fall into a 'performative contradiction' - a situation where one's actions imply that one holds a belief that contradicts one's stated views.

Cognitive relativism may carry certain practical advantages, such as fostering open-mindedness and tolerance. We may also be less inclined to assert opinions dogmatically.

Normative statements tell us what we OUGHT to do.

Normative epistemology - the attempt to determine which, if any, of our beliefs constitute genuine knowledge.

3 forms of this attempt are:

Foundationalism (Descartes) - the view that a belief constitutes knowledge only if it belongs to or can be deduced from a secure foundation of beliefs that are free from sceptical doubt.

Reliabilism - the theory that a belief constitutes knowledge when it has been arrived at though a process which we have good reason to regard as reliable.

Coherentism - the doctrine that a belief constitutes knowledge when it coheres satisfactorily with the rest of one's beliefs.

Normative epistemology tries to lay down norms or criteria that, if met, supposedly justify our calling a belief knowledge.

Relativists avoid these difficulties by refusing to grant any set of epistemic norms a special, privileged status (naturalised epistemology).


The attempt to naturalise epistemology is also open to a further, serious objection. Why should we not NOT be taking a critical attitude towards epistemic norms, asking questions like:

- Are the norms the best available?
- Could they be improved?
- Would other norms direct us more reliably towards truth?

Some of the most important advances in human knowledge have come from asking questions of just this sort.

Thinkers like Bacon, Galileo and Descartes made the scientific revolution possible by challenging the epistemic norms that had prevailed throughout the Middle Ages, arguing that reason, experiment and observation should take the place of scripture and other textual authorities.

'The elimination of the normative is attempted mental suicide' said Hilary Putnam, since it means giving up the attempt to improve our thinking.

Summary of the Theory of Knowledge

- The challenge of scepticism
- We can be certain about at least some of our subjective states (Descartes)
- Difficult to justify using our sense-impressions the basis for knowledge claims about a independent reality outside the mind
- Berkeleian idealism and phenomenalism try to avoid making the leap but hard to see how they can avoid solipsism
- Non-realism leads to relativism
- Relativism typically abandons the traditional epistemological search for norms that tell us when a belief really constitutes knowledge (normative epistemology)