When the 助動詞（じょどうし） (auxiliary verb)
だ is seen in its negative conjugated form, it states that (A) is not correct, but (B) is. This form is
ではなく, and may appear either with or without the 接続助詞（せつぞくじょし） (conjunction particle) て attached to the end.
ではなくて is commonly seen grouped with nouns, or other words that have been nominalized through the use of の or こと.
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事故（じこ）を起（お）こしたら逃（に）げるのではなくて、警察（けいさつ）に電話（でんわ）をしてください。
When you get into an accident, don’t run, but call the police please.
赤（あか）いのではなくて、青（あお）いのをください。
Please give me the blue one, not the red one.
今日（きょう）は暇（ひま）ではなくて忙（いそ）しいです。
It’s not that I am bored today, but busy.
メールではなくて、ファックスで送（おく）ってください。
Please send it via fax, and not email.
In
ではなくて, the 副助詞（ふくじょし） (adverbial particle) は is not strictly required. However, as this expression is comparing what (A) is ‘not’ to what (B) ‘is’, the contrast that は provides means that the phrase will sound far more natural with its inclusion.
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その建物（たてもの）は刑務所（けいむしょ）ではなくて、学校（がっこう）です。
That building is not a prison, but a school.
彼（かれ）は正社員（せいしゃいん）でなくて、アルバイトです。
He is not a full time worker, but a part time worker.
て sometimes performs in a similar way to a ‘comma’ in Japanese, allowing structures to appear together that usually wouldn’t. Due to this, if て is omitted from
ではなくて,
ではなく may not be linked directly to the next word, and a comma will be required. Regarding adjectives, this く form is known as the 連用形（れんようけい） (conjunctive form), and may only be linked directly with other 用言（ようげん） (conjugatable words), altering or adding to their overall meaning.
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このラーメンは不味（まず）いのではなく、味（あじ）が薄（うす）いだけです。
It is not that this ramen tastes bad, but it is bland.
私（わたし）は高（たか）いのではなく安（やす）いのを買（か）った。
I bought the cheap one, not the expensive one.