This is a mistake I habitually make, even though I know what the right form is.

Earlier tonight, I wanted to tell my friend "Let's go together!", so I sent a mail saying:


My friend sent back a mail :

はい、一緒{いっしょ}行{い}こう ;)

... reminding me that is incorrect, and is the appropriate particle in this case.

Which I know is right, but the reason it's stuck in my head to use is that it makes more sense to me.

is used to indicate direction of action(?), so I don't see how "going" can be directed at "together".

makes sense to me, because my understanding of is that it means "by use of" or "by way of" or something like that.

So to me it makes perfect sense to say 一緒{いっしょ}で行{い}こう because with it means "let's go, and the way we'll go is together".

Can someone help me break this habit by making some kind of logical sense of why is right and isn't?

3 Answers 3


First, we can't make the blanket statement that 一緒で is always incorrect, only that it is incorrect in this particular case.

Let's start by identifying how に is used here. In the case of 一緒に, に works the same way as in expressions like きれいに ("neatly", "prettily") and 気軽に ("casually"): it turns the preceding word into an adverb and shows how the action is done.

Because the point of 一緒 in the sentence 一緒に行こう is to show how the action is done ("together" as opposed to, say, "separately"), it must be followed by に.

On the other hand, で, when following a quantity or a noun identifying a group, expresses the range of the subject (such as in 一人で, 二人で, みんなで, and 家族で) and shows how many people/things participated in the action. 一緒 is too vague to be used with で in this sense, because it does not specify a number or a precise grouping.

But there are cases when 一緒 can be followed by で. This typically indicates that the parties involved are in the same physical location, but they may not be performing the same action. (In these cases, the line between the particle で and the ~て form of だ gets blurry.)

この会社では、社員は一緒で昼食をとる。 At this company, the employees have lunch together. [Implying that some may start eating a little before others, but everyone has lunch in the same place and at roughly the same time.] (incorrect)

友達と一緒でよかった。 I'm glad I was with a friend.

子供と一緒で荷物が多いと大変です。 It's tough when you're with your kids and you have a lot of luggage.

一緒 could also indicate that two things are the same; in this case, 一緒で can be replaced with 一緒であって:

彼は母校が一緒で、子供のころは毎日遊んでいた。 He went to the same school as I did, and when we were kids we played every day.

  • 3
    I think that この会社では、社員は一緒で昼食をとる。 is simply incorrect. Other than that, I agree with what you stated in this answer. Commented Jul 16, 2011 at 21:45
  • @Tsuyoshi: Hmm, can you elaborate on why it's incorrect? Is it a grammatical error, or just unnatural? Commented Jul 17, 2011 at 0:25
  • 3
    一緒で should be 一緒に in that sentence. I do not know if it is a grammatical error or not. Commented Jul 17, 2011 at 1:23
  • So, in a sense, would it be accurate to think of 一緒に as doing something "togetherly"?
    – Questioner
    Commented Jul 18, 2011 at 3:48
  • @Dave M G: "togetherly" sounds good to me. (And I'm tempted to start using "togetherly" just to see the reactions I'd get. :) Commented Jul 19, 2011 at 13:20

一緒に: adverb. Which means, it gives a description to an action (verb).

Went to the beach together with my little sister.

The verb 行く now has extra information: it was done together .

一緒で: predicate + conjuction. Which means, 一緒 is used to describe that the subject is together. Then is used to continue description with other predicate (description).

To borrow Derek's examples:

  1. 友達と一緒でよかった。




  1. 子供と一緒で荷物が多いと大変です。



(note: this split sentences are talking about self. The original joined sentences could be a general statement.)






This is only a speculation, but the etymology might be relevant. 一緒に derives from 一所に, which means 'at/to one place'. So the expression 一緒に行こう 'let's go together' is etymologically driven from 一所に行こう 'let's go to a single place'. In the latter, 一所 'a single place' is the destination, and hence you should use instead of . If that is just carried over to the usage of 一緒に, then it will make sense.

  • just to confirm you are saying that the kanji for issho has changed after it was introduced into the japanese language? Commented Jul 17, 2011 at 5:02
  • @Mark Yes. Most proably by folk etymology.
    – user458
    Commented Jul 17, 2011 at 11:50

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