1. SOURCE OF KNOWLEDGE Or OBSTACLE TO IT?
WAYS OF KNOWING
SOURCE OF KNOWLEDGE Or
OBSTACLE TO IT?

2. REASON This is a way of acquiring new knowledge about the world
We go beyond the immediate evidence of the senses

3. 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?

4. And the answer is……meet
Antony & Cleopatra
And Friday

5. 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

6. 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

7. 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
So, get your brains into gear and start thinking

8. 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

9. 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

10. The validity of an ARGUMENT is INDEPENDENT of the truth or falsity of the premises=
It gets worse!!

11. You can have false premises and true conclusions WHAT DO YOU RECKON THIS ONE IS?

12. 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

13. 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

14. 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 

15. 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

16. 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?

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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.

24. 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

25. 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