ではなく（て）・
This construction rejects one identification, description, or idea and replaces it with another: “not A, but B.” The rejected choice comes immediately before the construction, and the intended alternative normally follows.
Correcting the first choice
Think of this as a two-part correction. First, name the mistaken or rejected choice; then give the intended one. The second part may be a different noun, description, or account of what happened.
Three common patterns
The attachment changes according to what is being rejected.
これは会議室ではなく、資料室です。
This is not a meeting room; it is a document room.
AnalyzeA noun is rejected and replaced by another noun.
この町は静かではなくて、夜でもにぎやかです。
This town is not quiet; it is lively even at night.
AnalyzeThe na-adjective attaches without its final な.
電車が遅れたのではなくて、私が時間を間違えたんです。
It was not that the train was late; I got the time wrong.
AnalyzeThe entire first explanation is rejected, so the plain clause is followed by の.
With or without the linking ending
ではなくて links smoothly into the correction and is especially natural in flowing conversation. ではなく is more compact and can sound firmer, making it common in concise explanations and writing. Both forms can also occur in speech.
Choosing the ending
In conversation
In a neutral or more careful version, the correction would use 金曜日ではなくて.
How this differs from ordinary negatives and broad contrast
A standalone form such as ではない can simply say that something is not a particular thing. The present construction goes further by correcting or contrasting that choice with another. Meanwhile, が and けど can connect two broadly contrasting statements; they do not necessarily present the second statement as a replacement for the first.
More examples
これは故障ではなく、電池切れです。
This is not a malfunction; the battery is dead.
Analyzeそのホテルは不便ではなくて、駅から近くて便利でした。
That hotel was not inconvenient; it was close to the station and convenient.
Analyze彼は怒っているのではなく、少し疲れているだけです。
He is not angry; he is just a little tired.
Analyze注文したのは紅茶じゃなくて、コーヒーです。
What I ordered was not tea but coffee.
Analyze会議は中止ではなく、来週に延期になりました。
The meeting was not canceled; it was postponed until next week.
Analyze値段が高いのではなくて、今は買う必要がないんです。
It is not that the price is high; I simply do not need to buy it now.
Analyze