Is 〜たち used for groups of only two people?

Question

In a recent comment, Sjiveru wrote:

親たち isn't really valid for 'one's two parents', it means more of 'a group of parents (necessarily several families' worth)'. Outside of very modern uses with personal pronouns, たち can't be used for just two people.

To which mirka wrote a thoughtful reply:

Interesting, you'd never call your parents 親たち, but you would call your two children 子供たち, or your siblings お姉ちゃんたち, 弟たち, etc. I wonder why that is.

Is there a restriction on using 〜たち for just two people? If so, is this a rule with exceptions, as in mirka's comment?

Or is there a better explanation for why you'd never call your parents 親たち?

Answer 1

The single/plural duality of 親 as a concept is actually not that different from 子供, in that these phrases parallel each other:

• 親のいない家庭／子供のいない家庭
• 親同伴／子供同伴
• 親の目が届かない場所／子供の手が届かない場所
• 親に反対された／子供に反対された

I was thinking about this further, and noticed one good reason that 親たち is so infrequently used.

It is rude

親 is simply rude when referring actual parents, and not the concept of parent.

1. Within the family and with casual acquaintances, you are likely to refer to your parents by what you actually call them — 「お父さんお母さんどこ行った？」「パパたち帰ってきたよ」「お袋たちに聞いてみよう」. (〜たち is often suffixed to one of the parents to mean both parents)
2. To people you are on 敬語 terms with, you refer to your own parents humbly but politely, as 両親, 父母, 父と母.
3. People outside the family will refer to your parents politely, as ご両親, 親御さんたち, 親御さん方, お父様方, お母様方 etc. (〜たち is suffixed very naturally to 親御さん, the polite form of 親)

So, since actual parents are referred to politely, and the concept of parent already includes some sense of plurality, there is very little need for the word 親たち. It is only used to emphasize that you are talking about concept-parent in plural (i.e., sets of parents), and almost never used to talk about actual-parent in plural.

Answer 2

To answer the specific question: No, there is no restriction. You can use 〜たち with two people but you aren't exactly saying "two people", you are saying "groups of ~"; the definition given by JDIC being pluralizing suffix. 〜たち is used to refer a group and this group could very well include only two "animate objects" (or groups of "animate objects"); the number is indeterminate.

To specifically address what Sjiveru said: you would never call your own parents 親達. His point is valid in that 親 means parent/parents and if someone wanted to refer to their own parents as a group/couple, they would just say 親.

Referencing weblio for 親達 gives the following example.

息子が卒業すると親達が安心する。

The parents are made happy by their son completing his education.

and 親たち is used because the 親たち is not the speaker's own parents. You could just as well use 親 here but that would come off as, at least to my ears, as more direct and less polite.

As to why you would not use 親たち with your own parents, I don't have a concrete explanation. If I heard a native speaker refer to their own parents as 親たち, to my ears it would indicate some weird distance between the speaker and their parents. If you, as a non-native speaker, said 親たち in reference to your own parents, it would be understood by the context but it would be unnatural in the same way that non-native speakers overuse 私 and あなた in situations where the subject is already understood; they know you most likely have two parents, you don't have to add たち and (over) explain it to them.

Referring to mirka's comment, I also don't have a concrete answer. I suspect the reason is because 子ども does not have a "strong implication to mean a father + mother" like 親 does and so whether or not 子ども is being used as a singular or plural noun is less easy to determine from context. Also, in a lot of cases the specifics of 親 doesn't matter. If I tell my son he can't do something, he'll say to his friends:

親がダメと言った。

Whether 親 means father, mother, or both isn't important. His 親-figure said "no" and that's all that matters.

My guess is that with 子ども, in addition to the noun's person being harder to determine from context, whether or not it is plural matters more when understanding the sentence.

Answer 3

In this case, I think it's simply because we already have a specific and common word which refers to "one's both parents": 両親【りょうしん】. There is no reason not to use 両親 in formal situations.

I feel I sometimes hear (私の)親たちは旅行中だよ (instead of 両親は旅行中だよ) in casual conversations.