Induction

Induction

• Inductive arguments increase the strength of your belief in some fact– Inductive arguments are not truth-preserving

• What sorts of factors should increase your confidence in some fact?

Justifications

• Inductive arguments influence degree of belief

• Must keep track of why we believe certain facts– AI has a field of truth maintenance– Gilbert

• Facts are believed to be true by default

• They must be specifically marked as false

– There is a persistence of false-beliefs• Johnson & Seifert

• Information continued to influence people’s beliefs unless they were given a specific reason why it was false.

Coherence

• A coherent story makes beliefs stronger

• Pennington & Hastie– Story model of jury decision making

Category-based induction

Category-based induction

• Our category structures help us predict.

Bears have glutamate in their brainsHow likely is it that deer have glutamate in their brains?

Bears have glutamate in their brainsHow likely is it that deer have glutamate in their brains?

• How can you answer this question?– What if you know nothing about the property?

• These are called blank predicates

– What if you do have some relevant knowledge?

Induction with blank predicates• When we know nothing about the property,

we rely in similarities among categories

Bears have XHorses have X

Stronger Weaker

Bears have XBirds have X Similarity

Bears have XHorses have XLizards have X

Bears have XBirds have XLizards have X

Diversity

Bears have XMammals have X

Prairie Dogs have XMammals have X

Typicality

Similarity and coverage

• Why are these effects obtained?– Osherson, Smith, and colleagues

• Similarity-coverage model– The more similar the premise categories to the

conclusion, the stronger the argument– The better the premise categories cover the

category contained by the conclusion, the stronger the argument.

What about non-blank predicates?• Sometimes we know a little bit about the properties

– How does that affect induction?

• Heit and Rubinstein– Behavioral and morphological properties– Behavioral and morphological similarity

Stronger Weaker

Dolphins have antifreeze in their blood______________Sharks have antifreeze...

Foxes have antifreeze in their blood_____________Sharks have antifreeze...

Foxes are good trackersSharks are good trackers

Dolphins are good trackersSharks are good trackers

What if you know a lot?• Experts act differently than novices

– Similarity becomes far less important– Causal reasoning based on domain knowledge

• Premise diversity effects disappear in expertsWhite Pines get Disease XWeeping Willows get Disease XAll Trees get Disease X

River Birch get Disease YPaper Birch get Disease YAll Trees get Disease Y

• College students prefer argument on left– Consistent with diversity

• Tree experts prefer argument on right– Consistent with their causal reasoning.