This book defends the claim that a proper understanding of a physical theory requires knowledge of the relation between its rules and meaning. The author focuses on two main issues in the context of quantum mechanics and quantum logic: the completeness and the preservation of rules. The book presents new insights, including a reworking of Einstein's incompleteness argument, a fresh take on Bohr's correspondence principle, and several critiques of recent views in the philosophy of logic. This book will be of interest to scholars and students in the history and philosophy of quantum mechanics and logic.