Inductive logic

Inductive logicMoving from the specific to the general

What is inductive reasoning?

• Logic used to move from the specific to the general• E.g. “All Human Beings die” – creating a generalisation from

the observation that every known Human Being has died.• We use our past experience to reach

expectations/generalisations about the future e.g. In the past oranges have been good for me and boosted my vitamin C levels, so I infer that oranges are good me for.

• E.g. that chair has supported my weight in the past, so I infer that it will support me in the future..

• We use this type of inductive reasoning all the time, life would be impossible without it!

Language & inductive logic

• Language is effectively based upon inductive reasoning

• When we label things such as ‘dog’ or ‘table’ we are putting them into general classes and act according to our expectations of those ‘classes’ e.g. we don’t try to stroke a table! (or put things on the dog)

Science and inductive reasoning

• Metal A expands when heated, Metal B expands when heated, Metal C expands when heated…

• We formulate general laws based on our observations

Hasty Generalisations..• “Given a thimbleful of facts we tend to make

generalisations as large as a tub”• We tend to jump to conclusions based in

insufficient evidence.• A classic example is racial/national

stereotypes• Even well established generalisations can

sometimes let us down e.g. the bad piece of fruit that makes us sick, the chair that breaks etc.

Confirmation bias..• We tend to remember evidence that supports

our beliefs and forget/disregard evidence that contradicts them.

• E.g. “All Americans are loud” – we tend to focus on those Americans that confirm our existing prejudice and ignore the many who do not!

• This phenomenon my explain the ingrained nature of prejudice.

Think..hasty generalisations

1. Give three examples of your own of some hasty generalisations

2. Why do you think people are often so quick to jump to conclusions

3. What is the difference between a prejudice, a generalisation and a scientific law?

Uncritical inference..• Listen carefully to the story and then for each

statement read out determine whether that statement is true (T), false (F) or questionable (?).  A statement is to be considered true when there are statements in the story showing it to be true, false when there are statements in the story showing it to be false, and questionable when the story contains no direct evidence showing it to be unambiguously true or false.

The story

The statements1. Billy and Tom had been friends all of their lives.2. Both had doubts about their religious beliefs.3. The sniper spoke English well.4. Tom and Billy graduated high school together.5. When the sniper opened fire, Billy and Tom were side by side.6.  Tom walked with a limp.7. In his anger over Billy's death, Tom wanted to kill the sniper with his bare hands.8. Tom and Billy were unhappy in the Army.9. Had the sniper not lost his rifle when he tripped, he would not have wanted to surrender.10. Tom cleaned his rifle regularly.11. Camp Bingo was not in the United States.12. Camp Bingo was a dangerous place.13. The sniper was working alone.14. Another member of Billy and Tom's patrol stopped the sniper by shooting him as he was running off.15. Tom approached the sniper as he lay writhing in pain on the ground.

The answers..

Inference and photos

Wider angle..• It might have

been reasonably ‘infered’ from the previous picture that there was widespread support for the invasion

• This wider angle doesn’t disprove that, but it certainly doesn’t prove it either…

Inference from TV Ad’s

If you can’t see the video above go to: http://www.youtube.com/watch?v=OknElEusVhM

Uncritical inference• We assume (quite reasonably) that the ‘really

fast’ speed demonstrated in the advert is achievable

• Actually it isn’t possible under normal 3G conditions – it was staged for the advert

• So ‘uncritical inference’ can sometimes let us down..

Next lesson• Your task: to create a video, featuring

‘yourselves’ to explain in 3 minutes or less, in a simple and entertaining way, the principles and differences of deductive and inductive logic. Remember to include plenty of relevant, memorable and helpful examples!

• shown to the class on Tues 12 Jan.