 It can mean that John is married and either Mary is single or Joe is crazy, or else it can mean that either both John is married and Mary is single, or else Joe is crazy. An ambiguity like this, due to different ways to parse the same sentence, is sometimes called an “amphiboly”. If our formal language did not have the parentheses in it, it would have amphibolies. For example, there would be a “formula” \(A \amp B \vee\) C. Is this supposed to be \(((A \amp B) \vee C)\), or is it \((A \amp(B \vee C))\)? The parentheses resolve what would be an amphiboly.