A sentence A entails another sentence B if, whenever A is true, B must also be true. In this case we write:
There are different kinds of entailments. Part of the subject matter of this course is what the different kinds of entailments are. One distinction that's important is that an entailment may be true because of the laws of logic, or it may be true because of the meanings of the words involved. An entailment true because of the laws of logic is called logical entailment or a logical implication. . .
Of the entailments above only 4. is a logical entailment