It’s well known to anyone who has studied Japanese seriously that the language lacks a general concept of plurality, like English’s “-s”.
However, there are some cases where a plural modifier is used, as well as some other things to keep in mind about plurality which I’ll discuss in this post.
In many cases, a lack of a plural specifier isn’t too bad, as you simply use the word unchanged. For example,
- There are two dogs.
(Note: in this post I will start using brackets「」to contain the reading of certain kanji)
When translating statements like this back into English it’s easy, since you know there is more than one dog from the 二匹 part. Remember that -匹「ひき」is the counter used for dogs and some other animals.
There is another way to express “two dogs”, which is “二匹の犬”, and has a slightly different connotation than “犬が二匹”, in that it refers to the dogs as a group. Another example of this is the movie title “Seven Samurai”, 「七人の侍」。（This is something I read along time ago in a book or website, but it’s been so long I don’t remember the source to quote).
There are some cases where you brain really wishes there was a plural specifier. I’ll cite one which caught me off guard. I was sitting in traffic and heard the following Japanese:
At first I went looking for a specific car that was すごい（a word has a meaning close to “wow”), but then I realized this statement was referring to the large line of packed cars heading into the far distance. I’ve also heard すごい人 to refer to a big crowd of people. You can see for yourself on this Google image search if you like.
There is one category of words in Japanese where plurality does require a modifier, and you’ve probably already heard them: pronouns referring to people. These typically use -ら or -たち（達）when they are plural. I’ll give some examples, with the plural version on the right.
First person (“I”):
- 僕「ぼく」 ー＞ 僕たち、僕ら
- 俺「おれ」 ー＞ 俺たち、俺ら
- 私「わたし」 ー＞ 私たち
Second person (“You”):
- あなた ー＞ あなたたち
- きみ ー＞ きみたち
Third person (“He/She”):
- 彼女 ー＞ 彼女たち
- 彼 ー＞ 彼たち、彼ら
- こいつ ー＞ こいつら
The words これ・それ・あれ also can be made plural with -ら.
- これ ー＞ これら
- それ ー＞ それら
I have seen this most in formal writing and only rarely in casual speech, so I think its safe to use the normal forms (with -ら) even when talking about a plural concept.
The modifier -たち can also be applied general to other living things:
You might try to say “犬たちが２匹いる”, but that would be a bit unnatural or at least uncommon usage. In a case like this you can just use the singular form as I did in my first example above.
I’ve also seen -たち used for nonliving objects, like “ものたち” but I would not recommend using this pattern yourself unless you are very comfortable with how it is used.
As an interesting historical aside, -たち used to be used as a term of respect to address nobility and others with a high social status, but the meaning of respect is greatly diluted in modern Japanese.
There are also some words where a plural can be made by writing a word’s kanji twice. These I have only seen in literature and probably aren’t appropriate for most speech.
- 木々「きぎ」 – many trees
- 家々「いえいえ」- many houses
- 山々「やまやま」- many mountains
(In case you haven’t seen it before, the mark “々” means to duplicate the last character.)
Other vocabulary words related to singular/plural:
- 複数 「ふくすう」 - plural (a word used when discussing grammar, not used commonly in everyday speech)
- 単数 「たんすう」 – singular (this also is not used commonly in everyday speech)
- たくさん – many (more formal)
- いっぱい – many (less formal)
- いくつか – a few
- すう+counter or 何＋counter+か – a few (Ex: 数台、何台か for cars）
- 多い – many (adjective)
- 少ない – few (adjective)
- 数「かず」 – number (a count of something, not a number written somewhere which is 数字 or 番号）
Discussion on correctness of the word 友達たち (in Japanese), which briefly talks about the history of “たち”: http://www.nhk.or.jp/kininaru-blog/147629.html