Missives from a fly bottle
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Updated 14 July 2020
2. Another example

Here’s a second example, from the British philosopher Derek Parfit:
Just because something is natural it does not follow that we should do it, else we should not wear clothes.
I cannot recall where this crisp passage is from, but Parfit is obviously arguing for something, and a little reflection reveals that the structure of his reasoning is this:

Not wearing clothes is natural
If everything natural should be done, then we should not wear clothes It is false that we should not wear clothes
Not everything natural should be done

As you can see, it isn’t easy to extract the diagram from the passage, which is why this is a good test of logical ability!

Click here to temporarily hide the diagram if you’d like to try to reproduce it yourself from the original passage.

As mentioned, in this kind of exercise, one is not required to decide if the given argument is good or bad. Rather, the challenge is only to lay out its logical structure. These two skills should be distinguished because the test covers only one of them.