© michael lacewing justified true belief michael lacewing

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© Michael Lacewing Justified True Belief Michael Lacewing

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© Michael Lacewing

Justified True Belief

Michael Lacewing

Three kinds of knowledge

• Acquaintance knowledge– I know Oxford.

• Ability knowledge– I know how to ride a bike.

• Propositional knowledge– I know that elephants are heavier

than mice.

Justified true belief

• Analyses knowledge in terms of necessary and sufficient conditions

• ‘I know that p’:– The proposition ‘p’ is true;– I believe that p; and– My belief that p is justified.

Necessary and sufficient conditions

• Each condition is necessary for knowledge.• The three conditions together are sufficient for

knowledge.

The appeal of JTB

• I can’t know what is false.• I can’t know a proposition that I don’t

believe to be true.• Beliefs that are irrational or aren’t

based on the evidence aren’t knowledge.

The Gettier problem

• Justification is usually a matter of evidence, e.g. what I remember.

• Gettier: It is possible to have JTB without knowledge.

Infallibilism

• Since I can’t know something false, if I know that p, it is not possible that I could have made a mistake.

• Justified belief is true belief. If my belief could be false, then it is not justified.

• Is this too strong?

Development• Condition 4: My justification for

believing that p ‘stands up to the facts’.• I know that p if my justification for

believing that p is ‘undefeated’.

Objection

• Is this enough for knowledge?• Or should we consider what the facts

might have been?

That’s

Judy!

Case 1: Meeting Judy

That’s

Judy!

Case 2: Meeting Trudy

Reliabilism

• S’s belief that p is justified if and only if S’s belief that p is produced by a reliable process– Usually, this involves a causal connection

between p and the belief that p.

• Reliabilism rejects the view that justification requires evidence. It is not the grounds that the person is able to produce that make a belief knowledge; it is the source of the belief.

Reliabilism and Gettier

• My memory of where I put my watch is reliable in normal situations. But this way of knowing where my watch is is not reliable in a Gettier situation. So I don’t have knowledge.

• What about Judy and Trudy? Even though recognising people is normally reliable, I’d still think Trudy was Judy. So I’m not reliable at recognising Judy, because she has a twin living locally; so even when I recognise Judy as Judy, I don’t know it’s Judy.

Reliabilism and context

• If the process that caused my belief can’t rule out real alternative possibilities, then it isn’t sufficiently reliable for my belief to count as knowledge (or even as justified).

• Reliability is relative to context.