COMPLETING TRUTH TABLES

We need to be very systematic in completing a truth table that uses conventional rather than postfix notation. Think of it building from the inside out, as in the example below. What we always need to do is make sure we are representing every possible combination of values.

We begin by setting the alternating values for the variables.

(That) logic is easy only if everyone studies but not everyone studies implies logic is not easy.
T (logic is easy)
T (everyone studies)
F (everyone studies)
F (logic is easy)
T
F
T
F
F
T
F
T
F
F
T
T

Next we establish the value of the link for the proposition that sets up the initial relationship between logic being easy and having everyone study.

(That) logic is easy only if everyone studies but not everyone studies implies logic is not easy.
T (logic is easy) T T (everyone studies)
F (everyone studies)
F (logic is easy)
T F F
T
F
F T T
F
T
F T F
T
T

Now we need to see the two premises together. We set the value of the connective expressing their conjunction.

(That) logic is easy only if everyone studies but not everyone studies implies logic is not easy.
T (logic is easy) T T (everyone studies) F F (everyone studies)
F (logic is easy)
T F F F T
F
F T T F F
T
F T F T
T
T

The final step is to establish the value of the entire form by deciding the value of the implication. Keep in mind that every valid argument form can be expressed as a conditional, and a conditional (a proposition expressing implication) is false only when the antecedent is true and the consequent is false.

(That) logic is easy only if everyone studies but not everyone studies implies logic is not easy.
T (logic is easy) T T (everyone studies) F F (everyone studies) T F (logic is easy)
T F F F T T F
F T T F F T T
F T F T
T T T

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