SOURCE OF KNOWLEDGE Or OBSTACLE TO IT? 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

Three kinds of reasoning 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 http://www.rajeev.net.in/C-H.html So, get your brains into gear and start thinking

Deductive reasoning general - 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

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 It gets worse!! http://ftbelknap.org/PINK-PANTHER.html

You can have false premises and true conclusions WHAT 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 reasoning specific 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

Deduction vs. Induction 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

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

Coherence – more evidence is needed to support strange claims 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