Cognitive Psychology - Reasoning and decision-making.
Cognitive Psychology (PSY323M1)
Lecture11. Reasoning and decision-making.
Reading: Chapter 17 of Eysenck and Keane.
Your objectives are to:
i). Be able to outline the main theoretical orientations that account for deductive reasoning.
ii). Evaluate the empirical evidence from studies that have used Wason's (1966) selection task.
Often when we are thinking about something we're thinking about some past event or forthcoming activity of some sort - the sort of idle speculation and reminisence that fills much of our waking life. This type of undirected thinking can be contrasted with that which is more highly focussed, when for example we are required to work something out, to describe or explain something or draw a conclusion given certain premises. This type of thinking is described as directed thinking. Often in such latter situations what we are required to do is to take a piece of knowledge and actively transform it into a new piece of knowledge that is helpful in attaining a goal, whether simple or complex. And if you stop for a moment and devote a little time to appreciate some of the great achievements of human thought, the great intellectual endeavours of people like Albert Einstein or Marie Curie, you can't help but wonder at the real power of thought, and indeed at its great beauty. If you think about it the other way around, at the problem faced by a little human being, a child, that doesn't know very much at all about anything in our complex adult world, it is difficult not to be impressed at the speed with which he or she assimilates many different types of knowledge, at the inevitable and interesting mistakes the child makes while on its way to eventual mastery of different ideas, and the way in it copes with an understanding of the world that is in a constant and radical state of flux. So thoughts are wonderfully interesting.
How many times have you found yourself wondering what's going on in someone else's head? And why is it that when something makes sense to you that someone else won't buy it, or denies it, or thinks it's rubbish? You always think that you know, in whatever way you think you know these things, that you're right, or more right, or in some sense right - otherwise you'd never express an opinion, never voice an objection, never plan to get from A to B!
Of course we're not simply drawing on our memories when we think ...
This is a preview of the whole essay
How many times have you found yourself wondering what's going on in someone else's head? And why is it that when something makes sense to you that someone else won't buy it, or denies it, or thinks it's rubbish? You always think that you know, in whatever way you think you know these things, that you're right, or more right, or in some sense right - otherwise you'd never express an opinion, never voice an objection, never plan to get from A to B!
Of course we're not simply drawing on our memories when we think (although they are used), because every day brings something new, some new problem of one sort or another; and if it is genuinely new then we won't have a stored, well-prepared solution, but have to create one, that is, take what knowledge we have and create new knowledge. So how do we do that? How do we make the leap from one knowledge state to a new knowledge state? And do we do it rationally? That is, if we habe all the information available that we need to draw a conclusion, do we do it on a logical basis? If we know that A is true and B is true, how do we evaluate C?
Descriptive models: These describe a particular state of affairs. Most of the models that we have met so far describe mechanisms and/or processes that tell us something about the way in which some aspect of cognitive functioning actually takes place.
Normative models: In contrast these differ in telling us how we ought to do something, to perform some task to an optimum level. In studying reasoning and decision-making we can draw on logic which helps to specify how something ought to be done, how we ought to think in order to achieve a goal, and to identify the areas where our descriptive models violate those of normative models - because these violations indicate shortcomings in our reasoning.
Inductive and Deductive Reasoning
Inductive reasoning: this is a form of reasoning that suggests what is probably true, given our experience or knowledge of the situation. If you meet lots of people trekking through the streets laden with plastic bags late on the Saturday afternoon before Christmas you can conclude from experience that they've been Christmas shopping - although the conclusion is, of course, not certain!
Deductive reasoning: by contrast this form of reasoning draws a conclusion that must necessarily be true or false.
If the Earth circles a star at a distance of 93 million
miles
and the Earth circles the Sun at a distance of 93 million
miles
then the Sun is a star.
This conclusion must necessarily be correct. It demonstrates formal logic at work. The answer is not a question of being probably this or probably that! Things are either true or false - or no conclusion can be drawn.
Validity & Truth
An argument is valid if, and only if, the truth of the premises guarantees the truth of the conclusion.
Some taxpayers are foreigners Premises
No foreigners are citizens
Therefore some taxpayers are not citizens Conclusion
What is happening is that two or more assertions are integrated in order to deduce a new assertion that is a logical and necessary consequence. Deductions centre on 'logical words', as it were, for example quantifiers (e.g. all, some, none), connectives (e.g. and, or, if-then), and comparatives (e.g. more, less).
Validity, however, is not the same thing as truth. For example -:
If grass is pink or elephants fly, then the moon is square
Grass is pink
Therefore the moon is square
All assertions here are actually false, but the conclusion is nevertheless a valid one. Validity depends on the form of the argument, not its content. If the content is removed the argument can be expressed in abstract terms.
If p or q, then r
p
therefore r
Here the argument form is valid regardless of the actual truth of the statements
All dogs are animals
Some animals are pets
Therefore some dogs are pets
This syllogism is invalid, but since people know the truth of the conclusion they have difficulty with its evaluation. This is due to the challenge of separating the form of the argument from its content. It is rather easier to do when the fallacy of the conclusion is much more obvious, as in the following example.
All sharks are animals
Some animals are pets
Therefore some sharks are pets
People therefore exhibit 'belief-bias' effects. That is, they are biased to accept arguments that attempt to deduce a conclusion that they believe to be true, and to reject arguments that attempt to deduce a conclusion they believe to be false. This may not be too surprising, since in real life knowing what is true is more important than knowing what is valid.
Evaluating conditionals
Inference rules based on conditional statements are of two types , known as 'modus ponens' and 'modus tollens'. They take the following forms -:
If p then q
p Modus ponens
Therefore q
If p then q
Not q Modus tollens
Therefore not p
Modus ponens: the evaluation here seems easier and more intuitive, perhaps because a simple match is made. For example matching 'Friday' with 'Friday' in the following example guarantees the truth of the statement.
If it is Friday, then Bill is wearing a blue shirt
It is Friday
Therefore Bill is wearing a blue shirt
Modus tollens: the evaluation here is often found to be much more difficult, possibly because it includes negation. For example -:
If it is Friday, then Bill is wearing a blue shirt
Bill is not wearing a blue shirt
Therefore it is not Friday
Mary is 31 years old, single outspoken and very bright. Her degree was in philosophy. As a student she was deeply concerned with issues of discrimination and social justice, and also participated in anti-nuclear demonstrations.
Mary is Irish
Mary works in a bank
Mary works as a journalist
Mary is a lecturer
Mary has bright young daughters and a son
Mary is a treasurer in a branch of Greenpeace
Mary works in a bank and is an active feminist
Mary is a lecturer, a Samaritan and committed feminist