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Skip to 0 minutes and 7 seconds One way in which cognitive psychologists have attempted to understand how humans reason is by posing the question Is human reasoning like that of a logic machine? For present purposes the best example of a logical machine is a digital computer - your laptop is a digital computer. You switch it on and the electricity brings to life the computer’s critical software known as the operating system. The operating system is just one huge computer program that determines how the computer behaves. This kind of program sets out the logical steps that need to take place to ensure that the computer behaves appropriately.

Skip to 0 minutes and 46 seconds Now as long as the computer’s hardware is not faulty, every time you move the mouse to the left the cursor will follow. Computers invariably follow the rules as laid down in their operating system and logic machines invariably produce valid conclusions given the preconditions. If the claim is All men are mortal and the evidence is Harry is man then the logic machine will invariably record that the conclusion Harry is mortal is valid. So a key question is Do humans reason like logic machines? From last week, you ought to be on your guard about whether people are best characterised as being logic machines.

Skip to 1 minute and 33 seconds Remember our discussion of people being variable and tending not to reproduce the identical behaviour even when we try to reinstate the same testing conditions. On these grounds we would expect that at least some of the time peoples’ reasoning deviates from the rules of logic. And when this occurs we say they reason in an irrational way – their reasoning is irrational. But remember Humans do make errors and to err is to be human. This is a clear difference between us and logic machines – logic machines do not make reasoning errors. The picture is not so bleak however. Bear in mind that we humans are not completely irrational – we are not wrong all of the time.

Skip to 2 minutes and 15 seconds Scientific progress shows this to be true. The key questions for cognitive psychologists are therefore Under what circumstances do people reasoning logically? And of equal importance Under what circumstances do they reason illogically? Cognitive psychologists go further and ask how should we characterise their reasoning when they reason irrationally. What we as cognitive psychologists are trying to do is understand how and why humans make reasoning errors. If we can understand this then we can take steps to try and help them avoid similar errors in future.

There is 'logical' and there is 'psycho-logical'

Reasoning logically

What we are doing is exploring how readily people appreciate logical arguments and, hopefully, you will have been able to figure out that the fact that ‘I got wet’ does not necessitate the conclusion that ‘It’s raining’.

In fact, this particular puzzle is a classic example of an illogical, invalid argument. To explore this in more depth would take us further into logic and further away from the cognitive psychology of human reasoning.

For this reason, if you want to pursue this topic please use your favourite search engine type in ‘syllogisms’ and all will be revealed.

In moving forwards we will next consider how clearly there is more to human reasoning than logic!

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Introduction to Cognitive Psychology: An Experimental Science

University of York

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