Grammar is the system of rules by which words change form and combine into sentences — sounds (phonology), forms (morphology) and structures (syntax). Every lawyer works in two grammars: the relaxed grammar of speech (courtroom argument, client interview) and the exact grammar of writing (petitions, contracts, judgments).
Why grammar is a legal skill: a misplaced comma can cost millions (see Unit 3, 3.2); a wrong tense can misdate an event; a wrong article can change a generic statement into a specific one. Courts interpret what was written, not what was meant.