〜ついでに

A ついでに B: taking the opportunity of doing main task A, you also do side task B while you're at it: 買い物のついでに図書館に寄る (while out shopping, stop by the library). The pattern's requirement is that there MUST be a main task first — B is just something done alongside, on the way, with a little extra effort.

Connection: noun + のついでに; verb dictionary form when the main task is about to be done (駅へ行くついでに — while I'm heading to the station), た-form when the main task has been done (出張したついでに — taking advantage of that recent business trip).

ついでに can also stand alone at the start of a sentence as an adverb: ついでにこれもお願いします (while you're at it, this one too, please). In requests, this pattern noticeably softens the ask — the listener understands that what you're asking won't cost them a separate trip: 駅へ行くついでに、この手紙を出してくれませんか.

Examples

• 買(か)い物(もの)のついでに、図書館(としょかん)に寄(よ)って本(ほん)を返(かえ)しました。

  While out shopping, I stopped by the library to return some books.

• 大阪(おおさか)へ出張(しゅっちょう)したついでに、昔(むかし)の友達(ともだち)に会(あ)ってきました。

  While on a business trip to Osaka, I met up with an old friend.

• 駅(えき)へ行(い)くついでに、この手紙(てがみ)を出(だ)してくれませんか。

  Since you're going to the station anyway, could you mail this letter for me?

Related patterns

• 〜たび（に）