Talk about whether an action has already happened.
The rule
もう often means "already," and まだ "still" or "not yet." With the denial, まだ often indicates that an action is not accomplished.
Examples
もうたべました。
I've already eaten.
まだたべていません。
I haven't eaten yet.
Remember
- もう + accomplished; まだ + negation: "not yet".
- Talk about whether an action has already happened.
Common mistake
Consolidate まだ and もう in responses to a question about an action accomplished.