How to use a logic diagram

Posted: November 29, 2014 in Uncategorized

Venn logic diagrams

Ask a Philosopher

Rahul asked:

Suppose ‘no scientist are philosopher’ is true then which of these is true and which are false:

(i) no nonphilosopher are scientists
(ii) some nonphilosopher are nonscientist
(iii) all nonscientist are nonphilosopher
(iv) no scientist are nonphilosopher

Answer by Craig Skinner

The important thing here is to have a general method for solving this kind of predicate logic puzzle. Some people do it with the words, others with symbols, but it beats me how they manage.

Best is a diagram. Get pen and paper and follow these instructions (it’s much easier to do than the instructions suggest at first sight, I’d draw the diagram in this answer but my computer skills aren’t up to it).

* draw a square (this represents everything – philosophers, scientists, nonphilosophers, nonscientists)

* inside the square, draw a circle and put ‘P’ inside it – this circle is the philosophers

* also inside…

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