The notion of entailment is very useful in the study of sentence relations. It can be used to define all of the three semantic relations among sentences we have discussed so far. Table 6.9 presents how entailment can be used to describe the three types of semantic relationships.
Defining the sentence relations with the notion of entailment.
One sentence entails another if when the first is true the second is also true.
Two sentences are paraphrases of each other if they entail each other.
Two sentences are contradictory if one entails the negation of the other, and vice versa.