My understanding of 互いに 'mutually' or 'each other', while the auxiliary verb 合う usually means 'to/with each other'. I have seen sentences with them used together but also with only one and I'm wondering what the difference is.

For example:












1 Answer 1


From goo辞書: 互いに


And I think 合う: "to/with each other." is valid here.

Without contexts, it is bit hard to explain though, especially first example about dogs. Sorry for not being concise.

My interpretation is,

  • あの二匹の犬は互いに追いかけ合っています :

Two dogs are chasing each other in a way of circling around or back and forth, etc.

  • あの二匹の犬は互いに追いかけています。:

This one could be two dogs doing the same thing i.e in the same state. So, it might be two dogs chasing the same thing ex) Toy-Bones for dogs or something dogs tend to chase. So, it can be dogs are actually not chasing each other. But it still depends on the context. We know at least two dogs are "chasing".

  • あの二匹の犬は追いかけ合っています。:

I think this is the same as No.1. But in my perception of the reality, I tend to imagine this sentence as more static than the first one i.e. Dogs taking a rest and trying to catch the back of another dog if one has been caught and start the chasing-game again.

  • 私たちは月に一回互いにメール交換をし合っています。
  • 私たちは月に一回互いにメール交換をしています。
  • 私たちは月に一回メール交換し合っています。

I think the these three are equivalent in most cases. Using メール交換 makes what they are doing is more clearer. The last one is bit ambiguous. It can be exchanging e-mails to other than agents of the subject.

  • 彼らは互いに話し合っています。
  • 彼らは互いに話しています。
  • 彼らは話し合っています。

I think this one is close to No.1. First one describes one group having a conversation. Second one is bit ambiguous without the context. They are just talking to someone else other than themselves. i.e. in the same state. The last one can be same as first one, but it might be as same as dogs' example. It might not be dynamically talking to each other such as real-time conversation, but it may mean "negotiating". So, it can be more static and used as the concept.

  • 「彼らは互いに話しています」 can't mean they are talking to each other? I know 「互いに」 also as "with each other, reciprocally", which could imply that meaning. The examples from goo辞書 seems to me to have that meaning, but I'm not sure if that's because they also use 「合う」 (互いに顔を見合わす」 and 「互いに助け合う」).
    – Mauro
    Commented May 5, 2020 at 12:28
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    @Mauro Yes. It can be so. However, 互いに can mean 同じような状態にあるさま。: "in a similar state". For instance, I think 彼らは互いにスマホを見ている。is more likely that they are not seeing the same smartphone, but they are seeing their own smartphone. The predicate 話している is a bit ambiguous to me. It often means talking to each other, but it may mean they are calling to someone using their own smartphone. Commented May 5, 2020 at 12:49
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    2と3は互いに素 means 2 and 3 does not have any divisor other than 1. So, 2 and 3 are mutually independent prime number. Commented May 5, 2020 at 12:55
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    Ok, so if I'm understasting what you're saying, a sentence with just 「互いに」, without 「合う」, can both mean someone is doing something with another person (e.g., they are talking to each other), but it's more likely to see they are both doing the same thing (e.g. talking) with someone else?
    – Mauro
    Commented May 5, 2020 at 13:21
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    @Mauro I think it depends. I mean what is natural in the context explains the predicate. Without an auxiliary verb like 合う, I think 互いに話している is still likely to be talking each other in many cases. However, I believe 互いにスマホをいじっている。is more likely to describe that they are touching/using their own smartphone(It's bit weird to imagine touching one smartphone). I think 互いにスマホで話している is more likely to describe talking with someone else using their own smartphone (You do not have to use smartphone to talk each other in the same place). Commented May 5, 2020 at 13:37

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