まだ vs もう: Still, Yet, Already

もう and まだ look like a tidy pair — "already" and "still" — until you try to use them, and discover each one changes its English translation depending on whether the sentence is positive or negative. もう is "already" in a positive sentence but "not any more" in a negative one; まだ is "still" when positive but "not yet" when negative. Four English phrases, two Japanese words, and a mapping that will not sit still. This page is not the full tour of these adverbs — that lives on the もう and まだ time-adverb page — it is the decision: given a sentence, which one, and why the polarity flips the meaning.

The one idea: has the change happened?

Stop translating word-for-word and think about a change of state on a timeline. Every use of these two adverbs is a comment on one boundary: the moment the situation flips from an old state to a new one.

もう says the change HAS happened. まだ says the change has NOT happened yet.

That is the whole engine. Polarity — whether the verb is affirmative or negative — just tells you which state you have landed in. Lay the four combinations in a grid and the "unreliable" English glosses turn out to be perfectly regular:

Read the diagonal: もう食べた ("already ate") and まだ食べていない ("hasn't eaten yet") are the two natural poles of the same event — the transition either has or hasn't been crossed. Read the other diagonal: まだ食べている ("still eating") and もう食べない ("won't eat any more") sit on opposite sides of leaving the activity.

もう — the change is done

With an affirmative verb, もう reports that the event has already reached completion or that a new state is now in force.

With a negative verb, もう marks that you have left the old state — "no longer," "not any more."

まだ — the change hasn't come

With an affirmative verb, まだ says the old state is still running — nothing has flipped yet.

With a negative verb, まだ means "not yet" — the new state hasn't been reached.

The trap inside "not yet": it needs 〜ていない

This is the detail that catches nearly every learner, and it falls straight out of the state-change idea. "Not yet" is not a statement about a past event — it is a statement about the present: as of now, the change still hasn't happened. Japanese expresses a present, ongoing non-completion with the negative of the resultative 〜ている, i.e. 〜ていない — never the plain past negative.

Say ×まだ来なかった and you have not said "hasn't come yet"; you have said something like "still didn't come (back then)," anchored to a past moment — which is not what you mean. "Not yet" is a live, unfinished state, so it wants the 〜ていない form (see 〜ている vs 〜てある for why 〜ている carries this resultative sense).

The answer pattern that trips everyone

Because もう食べましたか literally frames the question around "already," learners feel pulled to answer もう — even when the answer is no. But "no" means the change hasn't happened, so the answer must switch to まだ.

The bare まだ (or the politer まだです / まだ食べていません) is the standard "not yet." A "yes" answer, by contrast, confirms the change: はい、もう食べました.

A second sense of もう: "more"

Keep one thing separate so it doesn't blur the grid: もう also means "more / additionally" in front of a quantity — もう一つ ("one more"), もう一度 ("once more"), もう少し ("a little more"), もうすぐ ("very soon, any moment now"). This is a different もう from the aspectual one, though they share the flavour of "and now, further."

Common mistakes

Mistake 1 — Answering "not yet" with もう. The question's もう does not carry over into a negative answer; "not yet" is まだ.

Mistake 2 — "Not yet" with the plain past negative. "Not yet" is a present unfinished state, so it needs 〜ていない, not 〜なかった.

Mistake 3 — Using もう for "still". "Still" is the old state persisting — the change hasn't happened — so it is まだ.

Mistake 4 — Using まだ for "not any more". "Not any more" means you left the old state — the change happened — so it is もう〜ない, not まだ〜ない.

Mistake 5 — Reaching for また ("again") instead of もう ("more"). For "one more" of a countable thing, it is もう + quantity; また means "again, on another occasion."

Key takeaways

• もう = the change has happened; まだ = it hasn't. That single question chooses the adverb.
• Polarity supplies the English: もう → "already" / "no longer"; まだ → "still" / "not yet."
• "Not yet" needs 〜ていない, never the plain past negative — it describes a present, unfinished state.
• In answers, a "no" to a もう…か question switches to まだ (まだです).
• Keep the quantity sense of もう ("one more," もう一つ/もう少し) mentally separate from the aspectual もう, and don't confuse it with また ("again").