まだ〜ていない

The pattern まだ〜ていない is the standard way to say "I haven't done [verb] yet" in Japanese.

1. Structure:
To form this, take the て-form of a verb and add いない (casual), いません (standard polite), or いないです (common spoken polite). The word まだ naturally appears at the beginning of the sentence or immediately after the topic/subject (e.g., 私はまだ... / 昼ご飯はまだ...). Note that when describing a situation or state that hasn't happened yet, especially outside your direct action, the subject often takes the が particle (e.g., バスがまだ来ていません - The bus hasn't come yet).

2. The Nuance of Expectation:
Unlike a simple negative like 〜ません, which just states a lack of action, まだ〜ていない focuses on the current state of non-completion. It strongly suggests that the action is planned, expected, or supposed to happen. For example, if you haven't eaten lunch but plan to, you use this pattern.

3. Responding to "Already":
This pattern is the standard negative response to questions using もう (Have you already...?).
Example: 「もう昼ご飯を食べましたか。」 (Have you already eaten lunch?)
Affirmative Response: 「はい、もう食べました。」 (Yes, I already ate.)
Negative Response: 「いいえ、まだ食べていません。」 (No, I haven't eaten yet.)

4. Still vs. Yet:
The word まだ changes meaning based on the verb. When used with an affirmative verb, it means "still" (e.g., まだ食べている - still eating). When used with a negative verb, it means "not yet" (e.g., まだ食べていない - not yet eaten).

5. Short Responses:
If someone asks if you have finished something, common short responses include:
• いいえ、まだです (Polite: No, not yet.)
• まだだよ (Casual: Not yet.)
• まだ (Very casual: Not yet.)

6. Comparison with まだ〜ない / まだ〜ません:
For volitional verbs (actions you control), まだ〜ていない means "haven't done it yet," while using the plain negative form (まだ〜ない) or its polite equivalent (まだ〜ません) means "won't do it yet" (e.g., まだ食べません - I won't eat yet). However, for verbs of arrival or completion (like 来る（くる） or 終わる（おわる）), using まだ〜ない (e.g., まだ来ない - hasn't come yet) is perfectly natural and commonly used to mean "hasn't happened yet."

7. Casual Contractions:
In daily conversation, the い in 〜ている is often dropped.
Example: 食べていない（たべていない） becomes 食べてない（たべてない）. This contraction is also extremely common in spoken polite Japanese, where 〜ていないです becomes 〜てないです (e.g., 食べてないです).

8. State Verbs and Exceptions:
Verbs that describe a state, existence, or potential (such as ある, いる, わかる, できる, 要る（いる）) do not use the 〜ていない pattern to mean "not yet." Instead, they use the simple negative (〜ない / 〜ません). For example, "I don't understand yet" is まだわかりません (not まだわかっていません), and "He isn't here yet" is まだいません.

Crucial Exception: The verb 知る（しる - to know）is a special case. While the affirmative "I know" is 知っている, the negative is always 知らない / 知りません. Therefore, "I don't know yet" is まだ知りません (or まだ知らない), never まだ知っていません.

9. Past Tense (Had Not Yet):
To express that you "had not done it yet" at a point in the past, simply change the ending to the past tense: まだ〜ていなかった (casual) or まだ〜ていませんでした (polite).

10. Change of State Verbs:
For verbs that describe a change of state, such as 結婚する（けっこんする - to marry）, using まだ〜ていない means you are not yet in that state. For example, まだ結婚していません translates to "I am not married yet" (literally: I have not yet entered the state of marriage).

11. Business and Formal Contexts:
In workplace or customer service situations, the humble form まだ〜ておりません is used instead of まだ〜ていません. For example, まだ確認しておりません（まだかくにんしておりません）means "I haven't checked yet" and is highly recommended for business emails and formal speech.