Knowledge

No number of observations can tell us anything with certainty about what we have not observed

Hume’s problem

David Hume (1711-1776)

Knowledge from induction

• Until the 17th century, Australians thought all humans were black

• They induced from observations of every human they met that all other humans were also black

• Notice that if you want to argue that inductive reasoning “just works!”…– Every time we have predicted a rise in

inflation because we have observed a rise in money supply, we’ve been right!

• This argument is itself an example of inductive reasoning

• We can’t say we’ve proved something is true if the proof assumed it was true

Hume’s problem

Popper’s solution• We gain knowledge not by observation

followed by inductive reasoning, but by conjecturing and then eliminating errors from our conjectures

• Thus all our knowledge consists in conjectures that have yet to be refuted

• We should not try to justify our knowledge (which is impossible) but to falsify it

“I may be wrong and you may be right, and by an effort, we may get nearer to the truth.”

- Karl Popper

Our knowledge is provisional and we are fallible

“Critical thinking, then, is the careful, deliberate determination of whether we should accept, reject or suspend judgement about the truth of a claim or a recommendation to act…”

Bruce Reichenbach (2001) Introduction to Critical Thinking

“There is no authority

beyond the reach of

criticism to be found within

the whole province of our

knowledge.”

Karl Popper

But do not confuse the authority of

power with the authority of

knowledge/expertise – your

manager can expect you to obey

company rules because she/he has

the power to enforce them.

See Whyte (2003) chapter 1

But she/he cannot expect you to

believe in the truth of a claim that

unions are unnecessary on her/his

say-so

Use of argument/reasoning

Use of argument with the intention

to justify acceptance of a claim is a

misuse But people do it

The decision to accept a claim is

always in the end driven by

emotion (or something else, but

not rationality or logic)

Use of argument/reasoning

To be rational is to be open to the

possibility of error and to be

critical to try to avoid error It is not to accept only justified

claims/proposals Argument is potentially useful in

criticising claims – it can highlight

contradictions and compel us to

revise our claims

Criticism

We need to be imaginative in our

criticism We need imagination to envisage

the implications of a claim or

proposal Then we look for contradictions

between the implications and other

claims that we accept as true

“The history of ideas… develops to an

indispensable degree on the basis of

criticism. A puts forward a theory, and

is then followed by B, who perceives

not only its value but some of its

shortcomings, and puts forward a new

theory which subsumes what is good in

A’s without containing its perceived

faults. Then along comes C, who does

exactly the same with B’s theory.”

Bryan Magee The Philosophy of Schopenhauer, p85