The tension between “eternity“ clauses and the possibility of constitutional replacement has been noted but not adequately explored. Constitutional theory must leave room for replacing a constitution with an eternity clause protecting some specific matter such as federalism or secularism with one modifying federalism or secularism, but then the sense in which the existing constitution is unamendable is unclear. Even more, a “simple“ amendment to a clause protected by an eternity provision might be adopted through the processes used to replace constitutions as a whole, in which case we might understand the simple amendment as a pro tanto replacement. Insisting that provisions protected by eternity clauses be modified by constitutional replacements — or through the procedures used for such replacements — might serve as valuable “speed bumps“ to slow down replacement, though one might wonder whether the eternity clause itself would be a sufficient speed bump.