だけでなく (an abbreviation of
だけではなく) is a common construction in Japanese which translates to ‘not only (A), but also (B)’. Sometimes the (B) statement may be left unsaid. This expression may connect to any (A) phrase that
だけ would usually be able to connect to.
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痩（や）せるためには運動（うんどう）をするだけでなく、食（た）べるものにも気（き）を付（つ）けなくてはいけない。
To lose weight, not only should you exercise, but you must also be careful of what you eat.
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名古屋（なごや）の夏（なつ）は暑（あつ）いだけでなく、湿気（しっけ）もひどい。
Summer in Nagoya is not only hot, but the humidity is terrible too.
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田舎（いなか）は静（しずか）かなだけでなく、空気（くうき）もきれいだ。
The countryside is not only quiet, but the air is also clean.
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トーマスは車（くるま）だけでなく、バイクとボートも持（も）っている。
Not only does Thomas own a car, but he also has a bike, and a boat.
The
で in
では is not the particle
で, but the 助動詞（じょどうし） (auxiliary verb)
だ in its 連用形（れんようけい） (conjunctive) form.
は is regularly dropped from
では expressions, or it may also be changed to
じゃ, for ease of pronunciation.
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タケルはピアノだけじゃなくギターも弾（ひ）けると聞（き）いた。
I heard that Takeru can not only play the piano, but also the guitar.
The 接続助詞（せつぞくじょし）
て should follow なく, as it is the conjunctive form of the
い-Adjective ない. However, the
て in this particular construction is very often omitted.
In writing, if there is no comma (known as a 読点（とうてん） in Japanese) after なく, the full
なくて construction will be required. When a comma is present, both forms are grammatically correct.
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角（かど）にあるラーメン屋（や）はおいしいだけでなくて量（りょう）も多（おお）い。
The ramen shop on the corner is not only delicious, but the portions are large too.