What is meant by semantically negative and structurally negative sentences?
Sentences in English may be negated (made negative) by negation markers or by sentence meaning. Negative markers are no, not, neither, none, nor, etc. Negative sentence meaning conveys negation through a variety of different means, for example, by using negating words such as decline, absent, renege, revoke, refuse, etc.
These two methods of sentence negation are called structural negation and semantic negation. Structural negation is when a sentence is negated (made negative) through negation markers: Al did not wish to see the film. The negative marker not is placed after the modal verb in the sentence of negation. These sentences of negation use a modal verb that precedes the negative marker: did not.
Semantic negation is when a sentence is negated through sentence meaning: Beatrice declined to be civil and amiable to Benedic. This can be paraphrased as Beatrice was not civil nor amiable to Benedic. This method of negation may be harder to understand because the negation is contained in the vocabulary rather than in easily recognized markers.
Another means of semantic negation is through ironic sentences that mean the opposite of what they directly say, for example, That will teach you to go on blind dates as paraphrased actually means, That will teach you NOT to go on blind dates.