In our fourth class of the critical thinking course we learnt how to represent an argument diagrammatically.
R1: Satellite pictures show a belt of very low pressure moving in from the Indian Ocean.
R2: Weather stations report huge clouds gathering in the northwest.Therefore,
C: Stormy conditions are likely to develop.
Here, R1 and R2 are two different reasons leading to a conclusion. So, the structure of the argument can be represented this way:
> C < R2
R1: The train leaves at 16:24
R2: It can take 40 min to get to the station
Therefore,C: We should set off by 15:40 to be on the safe side.
Here, both R1 and R2 together lead to the conclusion. So, the structure of the argument would be different from the last one. It would be:
R1 and R2
The single arrow shows that it is a combination of both the reasons that leads to the conclusion.
The arguments and the structure can get more complicated when there are more than two premises (reasons) in the argument. There may be a mixture of reasons that work in combination and reasons that work independently.
R1 : Rajinder was the only person, apart from me, who knew about Jed and Jill getting engaged.
R2 : I haven’t said a word.
R3 : The news is all around the college.
R4 : Rajinder spread a story about Daniel Li which I told him in confidence.
C : It is obvious that Rajinder cannot be trusted to keep a secret.
The first three reasons work together. The fouth reason is independent. This argument could be represented this way :
R1 and R2 and R3
> C < R4
So, we have seen how an argument works by unpacking or analyzing it, identifying its reasons and its conclusion and showing the structure.