4.131 strong assertion: 'could' with negatives and comparatives

'Could' is sometimes used in negative constructions with the comparative form of an adjective. You use 'could' like this to say that it is not possible for someone or something to have more of a particular quality.

• I couldn't be happier.
• You couldn't be more wrong.
• The setting couldn't have been lovelier.
• He could hardly have felt more ashamed of himself.