まだ

まだ is a versatile adverb that appears in several common structures. It is often contrasted with もう (already / no longer). A common point of confusion for English speakers is how to say 'not anymore'. Remember this core matrix:
• まだ + affirmative = 'still' (continuing state)
• まだ + negative = 'not yet' (continuing negative state)
• もう + affirmative = 'already' (changed state)
• もう + negative = 'not anymore / no longer' (changed state)
Do not use まだ to mean 'not anymore'.

1. With Negative Verbs (Not yet):
When used with action verbs, it typically takes the まだ〜ていない form to mean 'haven't done yet'. However, with state verbs, adjectives, and non-volitional verbs, the simple negative (ない form) is used.
Example 1 (Action): まだ食べていません（まだたべていません） (I haven't eaten yet).
Example 2 (State): まだ分かりません（まだわかりません） (I don't know yet).
Example 3 (Adjective): まだ寒くないです（まださむくないです） (It is not cold yet).
Note: Using an action verb with the simple negative (まだ食べない) means 'I am not going to eat yet'.

2. With Affirmative Verbs/Adjectives (Still):
When used with the ている form or state-indicating words, it means the current state is continuing. It can also be used with certain non-progressive verbs to mean 'still in time' or 'still possible'.
Example 1: 彼はまだ寝ています（かれはまだねています） (He is still sleeping).
Example 2: まだ間に合います（まだまにあいます） (We are still in time).
Example 3: まだ暑いです（まだあついです） (It is still hot).

3. With Nouns (Still):
It can attach directly to nouns to indicate that a status or condition is continuing.
Example: 私はまだ学生です（わたしはまだがくせいです） (I am still a student).

4. Remaining Quantity (Still more/Left):
It can indicate that a certain amount of time, distance, or quantity remains.
Example: まだあと五分あります（まだあとごふんあります） (There are still 5 minutes left).

5. With Numbers/Time/Age (Only/Just):
When used with quantities, time, or age, it can mean 'only' or 'just', emphasizing that the amount is small or early.
Example: 彼はまだ五歳です（かれはまだごさいです） (He is only five years old).

6. Comparative Usage (Still better/Still more):
When used with comparative words like より or the word まし (better/preferable), it indicates that one thing is 'still' better than another despite flaws.
Example: あっちよりはまだましです（あっちよりはまだましです） (It is still better than that one over there).

7. Emphasis (Still a long way):
The form まだまだ is often used for emphasis. It can mean 'still a long way to go' or is used as a polite, modest response when someone praises your skills.
Example: 「日本語が上手ですね」「いいえ、まだまだです」（「にほんごがじょうずですね」「いいえ、まだまだです」） ('Your Japanese is good.' 'No, no, I still have a long way to go.').

8. Standalone:
In response to a question like 'Have you finished?', you can simply say 「まだです」 to mean 'Not yet'.

Note on Orthography: まだ is almost always written in hiragana. The kanji form (未だ) exists but is generally reserved for formal or literary writing.