ReasoningFabian A. Soto

March 21, 2016

What is reasoning?

What is reasoning?Up to this point, we have discussed mostly how we

process information coming from the outside world

Our cognitive processes are also able to go beyond the

information given through thinkingWe can produce new mental representations on the basis

of previous representations

In reasoning, the previously held representations are

premises and the new representation is a conclusionthat follows logically from the premises.

There are two basic forms of reasoning

Here we will focus on deductive reasoning

Deductive reasoning tasks

Deductive reasoning tasks1. Syllogisms

They present premises like “all X are Y”, or “no X are Y”

Then they ask about whether a conclusion is true

For example:All men are mortalSocrates is a manSo, Socrates is mortal

2. Conditional reasoning

They present premises like “If X, then Y”, “If X and Y, thenZ”Then they ask about whether a conclusion is trueFor example:I parked in the street. If it rains outside, then my car willget wetIt rained outsideSo, my car got wet

What follows the “if” is called the antecedent“If it rains outside”: this is enough for your car to get wetWhat follows the “then” is called the consequent“Then my car will get wet”: this must be true to concludethat it rained, but not enoughFor example, you would not conclude this if nothing elseis wet

Human irrationality

Human irrationality

Our performance in these tasks systematically deviates

from what is expected by formal logic

We seem to be irrational

This is easier to see under some circumstances:

1. We are bad with negatives

Our performance drops when the premises contain NOT

or NO

If it doesn’t not rain outside, my car will not not get wet

My car is not wet

?

2. We are bad with abstract problems

Our performance drops dramatically when we go from

familiar examples to abstract problems

For example:

If X, then A is B

A is B

?

3. Our reasoning is biased by what we know

Sometimes we make judgements based on prior beliefsor general knowledge, instead than based on thepremises and the rules of logicThis is called belief-bias

People with higher IQs and more flexible thinking (easierto be swayed by good arguments) perform better

4. We look for evidence that confirms our beliefs

Sometimes we draw the wrong conclusions not because

of a failure in logic, but because of a problem with our

premises

For example, this happens in hypothesis testingWe use logic to determine how to test a hypothesis: “If the

hypothesis is true, then I should observe X”

However, we are biased to try to confirm our hypotheses:

confirmation bias

One way to study hypothesis testing is with Wason’s rulediscovery taskThe participant is presented with a triple, for example: 2,

4, 6

They have to think of a hypothesis about the rule

underlying the triple, for example: “three even numbers in

ascending order”

They have to propose a new triple to test their rule, for

example: 8, 10, 12

The experimenter gives feedback about whether or not

the new triple conforms to the rule

Rinse and repeat

The previous example is typical of people’s behavior: theytest their rule using a triple that conforms to it:

Can You Solve This?

Another hypothesis testing task is the Wason selectiontask

The Wason Selection Task - Four Card Problem Interactive Video

Antecedent: “If a card shows an even number on oneface”Consequent: “then its opposite face is blue”"Most people decide to affirm the antecedent (valid): pickthe even numberMost people avoid to deny the consequent (valid): pickthe the green cardSome people decide to affirm the consequent (invalid):pick the blue card

The duality of human thought

The duality of human thoughtSo on one hand, we are bad at formal reasoning, but on

the other, we are able to realize how bad we are

How is this possible?

An explanation comes from dual process theory (Evans,

1989)

We make mistakes because we use heuristicsThese are “quick and dirty” rules, work generally but not

all the time

A form of Type 1 processing: fast, automatic, no

awareness required

We can correct our mistakes because we use analyticthinkingThis is appropriate deductive reasoningA form of Type 2 processing: slow, controlled, requiresawareness and attention

Some variables produce a shift from analytic to heuristicreasoning (Evans, 2008):Time pressureWorking memory loadAgeCognitive abilityThis confirms that analytic reasoning, but not heuristicreasoning, is slow and uses executive functions

SummaryDeductive reasoning is studied with syllogism andconditional reasoning tasksPeople make many errors in these tasks: bad withnegatives, bad with abstract problems, belief bias,confirmation bias.Problems in deductive reasoning can be explained by theuse of heuristicsWe can correct our mistakes because we also haveaccess to analytical thinking