Metaphor: Which is as thin of substance as the air.
Shakespeare uses metaphors to convey his idea that the dreams that Romeo is dreaming are barely true. He does this by having Mercutio refer to dreams as unreliable and saying “which is as thin of substance as the air”. This proves that he is saying his dreams are flawed because air is not even visible and is so fine. Therefore Mercutio is saying that his dream unseeable and is unlikely. Although spite Romeos hesitation to attend the party, he decides to listen to Mercutio and take the gamble.