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Chapter 11

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McGill University
PSYC 213
Jelena Ristic

PSYC 213 Reading Group Summary CH 11: Nicholas Pasowisty Chapter 11 – Reasoning, Judgment, and Choice (pg. 327-357) Reasoning Syllogistic Reasoning - Reasoning  a process of thought that yields a conclusion from percepts, thoughts, or assertions o The ‘percepts, thoughts, or assertions’ are called premises - Exactly what makes a conclusion follow logically from the premises is not always an easy question to answer because there are different systems of logic – Aristotelian or syllogistic logic is older than others, and has been the subject of much psychological research – therefore a good place to begin - Syllogistic reasoning (sometimes called categorical reasoning)  a syllogism consists of two premises and a conclusion. Each of the premises specifies a relationship between two categories - Each premise in a syllogism can take any of four different forms: 1. Universal Affirmative  ‘All A are B’ o Notice that this premise might refer to a situation in which ‘All A are B, but some B are not A’ – this would be the case for a premise ‘All cows are animals’ o However, sometimes a universal affirmative premise refers to a situation in which ‘All A are B, and all B are A’ – this would be true for a statement such as ‘All right angles are 90-degree angles’ o This means that a universal affirmative premise may be understood by a person in different ways, even though from a logical point of view all possible ways of understanding a premise are equally important 2. Universal Negative  ‘No A are B’ o An important property to this premise is that their converse also is true – ‘No tomatoes are animals’ also means that ‘No animals are tomatoes’ 3. Particular Affirmative  ‘Some A are B’ o Notice that, although ‘Some A are B’, it may still be true that ‘Some A are not B’, or that ‘Some B are not A’ o Thus, it is true that ‘Some animals are not dangerous’ and that ‘Some dangerous beings are not animals’ o Nevertheless, particular affirmative premises may be converted – if ‘Some A are B’, then it is also true that ‘Some B are A’ o As counter-intuitive as it may seem, in logic, some means at least one, and possibly all 4. Particular Negative  ‘Some A are not B’ o Open to a number of specific interpretations o The converse of this is ‘Some B are not A’ – an inference that people often accept, although it is not necessarily true – it is true that ‘Some animals are not cows’ but it does not follow that ‘Some cows are not animals’ - It is important to understand that people may interpret premises in a variety of different ways, as we have seen in the above examples of different premises Logicism - Logicism  the belief that logical reasoning is an essential part of human nature - In illustrating their belief, logicists point to practical syllogism  occurs when the conclusion drawn from two premises becomes an action - An example of practical syllogism: o Premise 1: It is necessary for me to understand psychology as a whole o Premise 2: The only way to understand psychology as a whole is through the study of cognition o Conclusion: therefore, it is necessary to me to study cognition - Some argue that practical syllogism is not just something learned about in a cognition course, but ‘the natural mode of functioning of the conscious mind’  argue that we use this form of reasoning in everyday life – it is what most distinguishes human beings from other forms of life - A central concern in reasoning research is to determine the conditions under which participants will reason logically as well as the conditions under which participants reach conclusions in some other way o Talking about how a problem for logicism is that untrained participants make logical errors when asked to evaluate the validity of syllogistic arguments, while it is also true that the same participants do not always make logical errors and can make logically correct deductions at a level greater than chance The Effect of Content on Syllogistic Reasoning - The validity of a syllogism depends only on whether or not the conclusion necessarily follows from the premises – the truth or falsehood of a premise is irrelevant - It is natural to focus on the difference between believable and unbelievable invalid syllogisms - Evans, Handley, and Harper suggest that participants in a syllogistic reasoning task initially determine whether or not the conclusions is believable or unbelievable – if unbelievable, they then try to find some way of thinking about the premises that renders the conclusions invalid - If, however, the conclusion is believable, they do not try to determine if the syllogism is invalid, but rather try to determine if there is not some way of thinking about the premises that renders the conclusions acceptable - Thus, participants tend to set themselves the goal of discovering a syllogism to be invalid only if the conclusion is unbelievable The Interpretation of ‘Some’ - People reason according to the specific way they interpret the premises – the difficulty here is that people do not always work out all the possible interpretations of a set of premises - The way participants interpret premises that contain the word some provides a good example - Consider the statement ‘Some people are human’ o Although a true statement, it violates our feelings about the proper use of the word some o It seems to imply that ‘Some people are not human’ – although not one of the logically necessary implications of the statement, it seems to be because we ordinarily interpret the word some to mean ‘some but not all’ – use of the word some in this way is not using it strictly in the way dictated by logic o In logic, ‘some’ means ‘at least one and possibly all’ - An experiment by Begg (1987) found that for many people the word some carries with it the connotation of ‘less than the whole amount under consideration’ – of course, this is not the logical meaning of the word Mental Models and Deductive Reasoning - According to Johnson-Laird, people construct mental models of the situation to which a set of premises refers o Once constructed, people can draw conclusions that are consistent with the model o There are a number of possible mental models that can be derived from a set of premises o If a conclusions is consistent with all the mental models that are constructed, then it is accepted - The important thing about mental models is how the parts of the model go together o A mental model is a mental structure - What makes a syllogism difficult is that there may be a number of alternative mental models Relational Reasoning - Relational Reasoning  reasoning involving premises that express the relations between items, such as A is taller than B o Of particular interest are transitive relations – usually expressed by means of comparative sentences o The relation taller than is transitive because if ‘A is taller than B’ and ‘B is taller than C’ then ‘A must also be taller than C’ o Transitive relations typically come in pairs, one of which is the opposite of the other - Three-term series problem  linear syllogisms consisting of two comparative sentences from which a conclusion must be drawn o Example: ‘B is smaller than A’ and ‘B is larger than C’ – thus, C is the smallest and A is largest o This example illustrates the fact that mental models are iconic  meaning that the relations between the parts of the model correspond to the relations between the parts of the situation it represents o This example also illustrates a principle Goodwin and Johnson-Laird call emergent consequences  you can get more out of a mental model than you put into it - Parsimony  people tend to construct only one mental model if possible, and the simplest one at that An Alternative to the Mental Models Approach - Natural deduction system  a reasoning system made up of propositions and deduction rules to draw conclusions from these propositions - A common example under this system is that of the “Knight-Knave Problem” - A natural deduction system makes use of propositions stored in working memory o Propositions are statements built using connectives such as if…then, and, or, and not - The system makes use of deduction rules to draw conclusions from these propositions - Rules belonging to a natural deductions system (where p and q are propositions): 1. p AND q entail p, q  this rule means that if you have a proposition of the from p and q in working memory, then you can derive p and q as separate propositions 2. p or q and NOT p entails q  for example, if you have the propositions ‘A is a knight or B is a knight’ and ‘A is NOT a knight’ in working memory, then you can infer the proposition ‘B is a knight’ - A natural deduction system consists of psychologically basic inference rules – these are ‘elementary inference principles’ that participants rely on to solve reasoning problems - This approach is different from Johnson-Laird’s mental model approach  according to the natural deduction model, people carry out deduction tasks by constructing mental proofs – they represent the problem information, make further assumptions, draw inferences, and come to conclusions on the basis of this derivation (Rips, 1989) Wason’s Puzzles - Research on syllogistic reasoning is an example of an area in which a task familiar to a discipline other than psychology is studied in the hope that it will she light on psychological processes - Another approach is to invent reasoning tasks that directly tap interesting aspects of reasoning - Wason  his puzzles have been used in hundreds of studies – we will look at two of his inventions: the generative problem, and the card selection task The Generative Problem - According to Wason, a generative problem is on in which people do not passively receive information about a problem, but must generate their own information in order to solve it - Generative problem  participants are told that the three numbers 2, 4, 6 conform to a simple relational rule that the experimenter has in mind, and that their task is to discover the rule by generating sequences of three numbers. The experimenter tells them each time whether the rule has been followed - Participants in such an experiment tend to think that this task is more straightforward than it often turns out to be - At each trial, participants would write down a hypothesis about the rule – when trying to discover the rule, it is not a very good strategy to propose sequences that are consistent with your hypothesis about the rule, but rather propose a sequence that is inconsistent with your hypothesis - The appropriate strategy is to attempt to falsify your hypotheses, and thus eliminate incorrect beliefs – this is what Wason called an eliminative strategy - Wason’s experiments show a strong tendency on the part of ordinary people to engage in what is called a confirmation bias  tendency to seek confirmatory evidence for a hypothesis The Selection Task - Wason’s
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