です

です is a polite copula. Its primary roles are to link a noun or adjective to a topic or subject, to mark the entire sentence as polite toward the listener, and sometimes to substitute for a more specific verb when the context is clear (e.g., 私（わたし）はうなぎです - "I'll have the eel"). It is the polite equivalent of the casual copula だ used in plain speech (e.g., 学生（がくせい）だ vs 学生（がくせい）です). Note that you cannot stack them together; だ must be removed before adding です (e.g., 学生（がくせい）だです is incorrect).

Conjugations for Nouns and な-adjectives:
When using a な-adjective, you must drop the "な" before attaching です (e.g., 静（しず）かです, not 静（しず）かなです).

• Present Affirmative: です (is/am/are)
• Present Negative: ではありません or ではないです (formal/written), じゃありません (spoken), or じゃないです (modern spoken) (is not)
• Past Affirmative: でした (was/were)
• Past Negative: ではありませんでした or ではなかったです (formal/written), じゃありませんでした (spoken), or じゃなかったです (modern spoken) (was not)

Usage with い-adjectives:
Unlike nouns, い-adjectives conjugate themselves for tense and negation. In these cases, です is added to the end without changing its form purely to provide politeness. For negative and past negative, you can also use the slightly more formal 〜くありません and 〜くありませんでした.

• Correct: 寒（さむ）いです (It is cold)
• Correct: 寒（さむ）くないです / 寒（さむ）くありません (It is not cold)
• Correct: 寒（さむ）かったです (It was cold)
• Correct: 寒（さむ）くなかったです / 寒（さむ）くありませんでした (It was not cold)
• Incorrect: 寒（さむ）いでした

Important Rule for Verbs: You cannot attach です directly to plain affirmative or plain past tense verbs (e.g., 食べる（たべる）です and 食べた（たべた）です are incorrect). To make a verb polite, you must use the ます form (e.g., 食べます（たべます）), the polite past (e.g., 食べました（たべました）), or the explanatory んです (e.g., 食べる（たべる）んです / 食べた（たべた）んです). However, です can be attached to the plain negative form and the plain past negative form of verbs (e.g., 食べない（たべない）です and 食べなかった（たべなかった）です).

Forming Questions:
To turn a statement into a question, simply add the question marker か to the end of です (forming ですか). You do not need to change the word order.

• 学生（がくせい）ですか？ (Are you a student?)
• 高（たか）いですか？ (Is it expensive?)

Pronunciation Note: In standard Japanese, the final 'u' is often silent (devoiced), so the word ends on the 's' sound.