This book proposes and motivates a ban on words and sentences of a particular form, and shows that there are differences between how this ban is satisfied at the word level and at the sentence level. One striking finding is that syntactic operations may serve as a means of avoiding violation of the ban, which might not be expected on a strictly feed-forward grammatical architecture. A theoretically interesting consequence of this is that the syntax must be able to see at least some information that the phonology can access, motivating an architecture of the grammar that is different from what is commonly assumed. Empirically, this ban can account for a variety of apparently disparate linguistic facts including, but not limited to: cross-linguistic skews in attested stress patterns, morphophonological differences between prefixes and suffixes, restrictions on certain disharmonic word orders and cases where this restriction is apparently lifted, and a requirement that heavy elements undergo obligatory extraposition from a variety of fronted constituents. Each of these cases can be understood as the consequence of the grammar of a particular language employing a limited set of strategies to ensure that the proposed ban is satisfied.