〜ませんでした is the polite past negative form. It means “did not” and is used for actions that did not happen in the past. Key points: • Replace ます with ませんでした to make past negative • Polite and clear for everyday speech • Often used with time words like 昨日 or 先週 • Same word order as other ます-form sentences For example, “行きます” becomes “行きませんでした” (did not go). “食べます” becomes “食べませんでした” (did not eat). Time words make the meaning obvious: “昨日行きませんでした” means “I did not go yesterday.” This form is longer, but it is regular and easy to build. Just take the ます form and replace it with ませんでした. Practice by making pairs: 食べました / 食べませんでした, 行きました / 行きませんでした. This helps you switch between past and past negative smoothly.