This document discusses common grammar fallacies, or false ideas about linguistic rules. It defines grammar fallacies and examines four specific examples: the idea that some languages have no grammar; that simplicity or complexity determines a grammar; that grammars should be logical and analogical; and that spoken and written language grammars are equivalent. While languages have differing levels of complexity, all languages have underlying rule systems or grammars that govern their structure and use. Grammars also naturally contain some irregularities that arise over time.