WAYS OF KNOWING. SOURCE OF KNOWLEDGE Or OBSTACLE TO IT?. REASON. This is a way of acquiring new knowledge about the world We go beyond the immediate evidence of the senses. So, how good is your reasoning?. A man rides into town on Friday, he stays three night and leaves on Friday. HOW?
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WAYS OF KNOWING SOURCE OF KNOWLEDGE Or OBSTACLE TO IT?
REASON • This is a way of acquiring new knowledge about the world • We go beyond the immediate evidence of the senses
So, how good is your reasoning? • A man rides into town on Friday, he stays three night and leaves on Friday. HOW? • Antony and Cleopatra are lying dead on the floor of a villa in Egypt. Nearby there is a broken bowl. There is no mark on either of them and they were not poisoned. HOW DID THEY DIE?
And the answer is……meet Antony & Cleopatra And Friday
Finally Rationalism and certainty? • All human beings are mortal • Socrates is a human being • It necessarily follows that Socrates is mortal • No if’s’ or but’s’, no opinions, nothing to do with culture • Given the assumptions or premise the conclusion has to follow http://www.sru.edu/images/philo-socrates.jpg
What is rationalism? • The central tenet is that we can discover important truths through reason alone • Rationalist like • Logic ] certain and useful, • Maths ] unlike empiricism http://almez.pntic.mec.es/~agos0000/descarte.gif http://www.redmolotov.com/images/designs/cogitoergosum_design.jpg
There are three kinds of reasoning Deductive Inductive Informal All have serious fallacies – invalid patterns of reasoning that need to be considered and guarded against So, get your brains into gear and start thinking Three kinds of reasoning http://www.rajeev.net.in/C-H.html
Deductive reasoninggeneral - specific • All apples are fruit • Some apples are red • Therefore • Some fruit is red This is a syllogism • Syllogisms have • 2 premises and a conclusion • 3 terms that each appear twice • QUANTIFIERS – all, some, no – the quantity that is being referred to
Truth and validity – crucial diff • These are NOT the same thing • Truth = what is the case, it is • property of the statement, • validity of arguments • Validity = whether the conclusion follows the premises • So an argument is valid or invalid NOT true or false STAY WITH ME ON THIS ONE
It gets worse!! • The validity of an ARGUMENT is INDEPENDENT of the truth or falsity of the premises + = http://www.lateinamerika.de/Laender/images/bolivien/Che_Guevara.jpg http://www.astrologyweekly.com/natal-charts/images/che-guevara.php.jpg http://ftbelknap.org/PINK-PANTHER.html
You can have false premises and true conclusionsWHAT DO YOU RECKON THIS ONE IS? http://www.caradisiac.com/media/images/le_mag/mag196/eric_clapton_196.jpg http://catsinsinks.com/images/cats/42b0938bbf875.jpg http://www.the-academy-of-music.com/lessons.html
Mission Impossible is – valid argument with true premises and false conclusion • In groups of 4 people • Construct syllogisms that have • 2 true premises, and a true conclusion • 1 true premise, 1 false premise and a true conclusion • 1 true premise, 1 false premise and a false conclusion • 2 false premises, and a true conclusion • 2 false premises, and a false conclusion http://flatrock.org.nz/topics/animals/assets/black_widow_spider.jpg
Argument structure • Pure logic is concerned with the structure of the arguments not the content • All dogs are mammals • Some dogs are Boxers • THEREFORE – some mammals are Boxers • This reduces to • All A’s are B • Some A’s are C • Therefore some C are B’s • This abstraction helps avoid belief bias – belief that an argument is valid because we agree with the conclusion
Venn diagrams, should help with this • Syllogisms are no easy matter to sort – Venn diagrams can be used to help (Maybe) • You build up the Venn diagram from the premises then you can work out if the conclusion is correct • Now you try • All A’s are B’s • All B’s are C’s • Therefore all C’s are A’s BEWARE
Over to you again • Use Venn diagrams to state whether each of these are valid or invalid • All Italians eat spaghetti • Giovanni Rossi eats spaghetti • Therefore Giovanni Rossi is Italian • No Martians have red noses • Rudolph has a red nose • Therefore Rudolph is not a Martian • Some monks are Tibetan • All Tibetans are good at Yoga • Therefore some monks are good at yoga
And in conclusion (just in case your not totally confused) • Just because the argument is valid – it does not mean the conclusion is true • For the conclusion to be true you must be able to answer yes to both of these • Are the premises true? • Is the argument valid?
The premise is obvious = assume the rest • In everyday life we rarely argue formally and some things are missing BUT WHAT • Jenny goes to Oxford University, so she must be very intelligent • Graham is a politician so he is probably lying • Since it is natural to eat meat there is nothing morally wrong with it
However!! • Deductive reasoning preserves the truth – it is NOT a source of truth • All human beings are mortal • Socrates is a human being • Therefore Socrates is mortal • This is true if the premises are true – knowledge of mortality is not from reasoning it is based on experience AND SO TO
Inductive reasoningspecific to general • How do we know humans are mortal? • All humans in history have died therefore through inductive inference we move form the observed to the unobserved • All observed humans are mortal so ALL humans are mortal • We use this all the time in everyday life • Past experience shapes our expectations
Language is based on inductive reasoning • HOW? • My cat gets excited when I go to the fridge • is he using inductive reasoning? • Do animals reason? • Or is it something else? SCIENCE USES INDUCTIVE REASONING It formulates general laws from observations
General – particular Example Water is a liquid Liquids turn to a gas when heated Water will turn to a gas if heated Value More certain, less informative Particular to general Example Liquid A turns to a gas when heated, liquid B turns to a gas when heated etc All liquids turn to gas when heated Value More informative but less certain Deduction vs. Induction
How reliable is inductive reasoning? • The problem here is hasty generalisation • Sexism • Racism • What is the boiling point of water? • Hasty generalisations are made worse by confirmation bias http://www.paistortuga.net/binladillas/wtc/arabs-muslims.jpg
What hasty generalisations do you make? • Are prejudice, generalisations and scientific law different? Read this carefully A businessman has just turned off the lights in the store when a man appeared and demanded money. The owner opened a cash register . The contents of the cash register were scooped up and the man sped away. A member of the police force was notified promptly.
Good or bad generalisation? • Certain criteria make for more reliable generalisations • Number – see 1 dog swimming it is not enough to conclude that all can swim • Variety – various circumstances, different breeds of dog, young, old http://www.dadspetcare.com/dogs/images/Dog_product.jpg http://www.csus.edu/indiv/f/foxs/ccn/images/doggy-dip3.jpg
Exceptions – avoid confirmation bias and actively look for counter-examples, ask friends for them? • Coherence – more evidence is needed to support strange claims • Subject area – natural sciences are more likely to yield reliable generalisations than human sciences http://www.cathouse-fcc.org/africa03/wdog.jpg http://www.freewebs.com/ronaldowen/Dogs%20Can%20Fly.jpg