1. Knowledge No number of observations can tell us anything with certainty about what we have not observed Hume’s problem David Hume (1711-1776)

2. Knowledge from induction Until the 17 th century, Australians thought all humans were black They induced from observations of every human they met that all other humans were also black

3. 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

4. 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

5. “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

6. “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

7. “There is no authority beyond the reach of criticism to be found within the whole province of our knowledge.” Karl Popper

8. 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

9. 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)

10. 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

11. 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

12. “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