Semantic

• The relationships between sentences:

Sentences can also be semantically related to one-another in a few different ways.

Semantic relationship	Definition	Example
Paraphrase	One relationship that two sentences can have with each other is being paraphrases of each other. This is a good example of how we all understand semantics already on some level because people can easily tell when a sentence is a paraphrase, because when two sentences are paraphrases of each other, even though the form is different you will understand the same meaning from them. Paraphrases have the same truth conditions; if one is true, the other must also be true.	'The boys like the girls' and 'the girls are liked by the boys', 'John gave the book to Chris' and 'John gave Chris the book'.
Entailment	Entailment is a little more tricky than paraphrase in that the two sentences don't mean exactly the same thing, instead, when one sentence entails another, for the second sentence to be true, the first one must be true. There are two different types of entailment.
Mutual entailment	When each sentence entails the other, i.e. each sentence must be true for the other to be true.	'John is married to Rachel' and 'Rachel is John's wife', 'Chris is a man' and 'Chris is human'.
Asymmetrical entailment	With asymmetrical entailment, only one of the sentences must be true for the other to be true, but that sentence may be true without the other sentence nescessarily having to be true.	'Rachel is John's wife' entails 'John is married' (but John is married does not entail Rachel being his wife), 'Rachel has two brothers' entails 'Rachel is not an only child' (but Rachel not being an only child does not entail Rachel having two brothers).
Contradiction	Sentences can also be semantically related when they contradict each other. Sentences contradict each other when for one to be true the other must not be.	'Rachel is an only child' and 'Rachel's brother is called Phil', 'Alex is alive' and 'Alex died last week'.