1987
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:

> 一緒{いっしょ}`で`行{い}こう！

My friend sent back a mail :

> はい、一緒{いっしょ}`に`行{い}こう `;)`

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

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

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

`で` makes sense to me, because my understanding of `で` 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 `で` 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 `に` is right and `で` isn't?
CC BY-SA 3.0
2011-07-16T15:13:31.530
1985
2014-06-03T02:37:59.513
2014-06-03T02:37:59.513
119
119
question
grammar particle-に particle-で
Why is 一緒に correct and 一緒で incorrect?
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.
CC BY-SA 3.0
2011-07-16T16:54:55.250
1987
2011-07-17T17:53:37.393
2020-06-17T08:18:27.500
-1
94
1985
answer
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 `に` instead of `で`. If that is just carried over to the usage of
`一緒に`, then it will make sense.
CC BY-SA 3.0
2011-07-17T02:50:21.150
1992
2011-07-17T02:50:21.150
1985
answer
`一緒に`: adverb. Which means, it gives a description to an action (verb).

> 妹と一緒に浜辺へ行きました。  
>  _Went to the beach together with my little sister._

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

`一緒で`: predicate + conjuction. Which means, `一緒` is used to describe that the
subject is together. Then `で` 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。
>

becomes

> 友達と一緒でした。それで、よかったです。

and

>   1. 子供と一緒で荷物が多いと大変です。
>

becomes

> 子供と一緒です。また、荷物が多いです。すると、大変です。

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

and

> 彼は母校が一緒で、子供のころは毎日遊んでいた。

becomes

> 彼は母校が一緒だ。子供のころは毎日遊んでいた。
CC BY-SA 3.0
2011-07-17T11:45:02.160
1997
2011-07-17T12:03:56.303
2011-07-17T12:03:56.303
15
154
1985
answer