Logical and tautological equivalence
In the last chapter we discussed the notion of logical equivalence.
We say that two sentences are
logically equivalent when they have the same truth values in every possible circumstance.
In this chapter, we want to discuss tautological equivalence, which is a certain type of logical
equivalence.
Two sentences are tautologically equivalent if they can be seen to be equivalent
simply in virtue of the meanings of the truthfunctional connectives.
We can check for
tautological equivalence using truth tables.
Suppose we want to know if two sentences are tautologically equivalent.
We need to construct a
truth table with reference columns for each atomic sentence that appears in our two sentences.
Then, to the right of the reference columns we need to place the two sentences in question.
Once
the truth table is complete, we check for tautological equivalence by looking to the columns under
the main connectives in each of the two sentences.
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 Fall '06
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 Logic, Logical connective, Tautological Equivalence

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