Long ago, onaji was like all the other adjectives. It wasn’t the only one that ended in /ji/. All the other ones, though, evolved to end in /jii/ instead. It is for this reason we have adjectives like susamajii 凄まじい (fierce/tremendous) and mutsumajii 睦まじい (harmonious). Had it remained as onashi like it was even further back in time, it might be just like all the other adjectives, but now its conjugations are hybrid between adjectives and adjectival nouns.
| Form | Plain Speech | Polite Speech |
| Non-Past | 同じだ Onaji da | 同じです Onaji desu |
| Past | 同じだった Onaji datta | 同じでした Onaji deshita |
| Negative | 同じ｛では・じゃ｝ない Onaji [de wa/ja] nai | 同じ｛では・じゃ｝ないです Onaji [de wa/ja] nai desu 同じ｛では・じゃ｝ありません Onaji [de wa/ja] arimasen |
| Negative Past | 同じ｛では・じゃ｝なかった Onaji [de wa/ja] nakatta | 同じ｛では・じゃ｝なかったです Onaji [de wa/ja] nakatta desu 同じ｛では・じゃ｝ありませんでした |
| Before Nouns | 同じ Onaji | |
| Before Nominalizer No の | 同じな Onaji na | |
| Adverbial Form | 同じ Onaji 同じく Onajiku 同じに Onaji ni 同じように Onaji yō ni | |
| Te て Form | 同じで Onaji de | 同じでして Onaji deshite |
Although its conjugations are more or less an amalgam of adjectives and adjectival nouns, some of its forms deserve extra addition, and because this is the case, we will spend a little more time seeing how its various forms are used.
Typical Conjugations
1. 結果は同じだったよ。
Kekka wa onaji datta yo.
The results were the same.
2. ずっと同じじゃないですか。
Zutto onaji ja nai desu ka?
Is it not always the same?
3. 日本語と同じですね。
Nihongo to onaji desu ne.
It’s the same as Japanese, huh.
4. これは人間と同じで、一番多いのは、ガンです。
Kore wa ningen to onaji de, ichiban ōi no wa, gan desu.
This is the same as humans, and the most common is cancer.
5. 昨日とおんなじだよ。
Kinō to on’naji da yo.
It’s the same as yesterday.
Pronunciation Note: Onaji may also emphatically be pronounced as /on’naji/.
Before Nouns
6. 彼は、1年間くらい同じ服を着ていました。
Kare wa, ichinenkan kurai onaji fuku wo kite imashita.
He wore the same clothes for about a year.
7. ほぼ同じ意味です。
Hobo onaji imi desu.
It has almost the same meaning.
8. 僕たちは同じ学校に通っています。(Male Speech)
Bokutachi wa onaji gakkō ni kayotte imasu.
We go to the same school.
9. 皆同じ穴のムジナだな。
Mina onaji ana no mujina da na.
They are all birds of a feather.
Phrase Note: The Japanese expression for this is literally “badgers of the same hole.”
10. 私たちは同じ年に生まれました。
Watashitachi wa onaji toshi umaremashita.
We were born in the same year.
11. 私は同い年の人と結婚しています。
Watashi wa onaidoshi no hito to kekkon shite imasu.
I’m married to someone of the same age.
Phrase Note: Onaidoshi 同い年 is a set phrase meaning “the same age.”
Before Nominalizer No の
When the particle no の is used in turning what precedes into a noun phrase for whatever reason, if onaji 同じ is what’s directly before it, na な must intervene. We’ve already seen how no/n desu (ka) の・んです（か） is used in sentences in seeking an answer, and we learned how na な is needed with adjectival nouns. In this case, onaji 同じ functions like any other adjectival noun.
12. 音質は、CDと同じなのです。
Onshitsu wa, shiidii to onaji na no desu.
That’s because the sound quality is the same as a CD.
13. 何故、惑星の公転方向は同じなんですか。
Naze, wakusei no kōten hōkō wa onaji na n desu ka?
Why is it that the direction of revolution for the planets is the same?
14. 服装が同じなので、見分けがつきにくいですね。
Fukusō ga onaji na node, miwake ga tsukinikui desu ne.
Their clothes are the same, so it’s hard to distinguish them, huh.
Particle Note: The particle node ので is composed of the particle no の and the te て form of da だ. Put together, node のでmeans “because.”
Adverbial Form: Onaji ni 同じに
15. 私達の結果と同じになりました。
Watashitachi no kekka to onaji ni narimashita.
(Their results) became the same as our results.
16. 全部同じに見えます。
Zembu onaji ni miemasu.
They all look the same.
17. 実印と銀行印を同じにすることはできるんですか。
Jitsuin to ginkōin wo onaji ni suru koto wa dekiru n desu ka?
Is it possible to have one’s registered seal the same as one’s bank transaction seal?
Adverbial Form: Onaji yō ni 同じように
This form has a meaning of “similarly/like.”
18. スパゲティをレシピと同じように作った。
Supageti wo reshipi to onaji yō ni tsukutta.
I made spaghetti like the recipe.
19. 猫からは周囲が人と同じように見えますか。
Neko kara wa shūi ga hito to onaji yō ni miemasu ka?
Do one’s surroundings look the same from a cat’s perspective?
20. 普通の人と同じように仕事が出来ません。
Futsū no hito to onaji yō ni shigoto ga dekimasen.
I can’t work like normal people.
21. 過去と同じように設定してください。
Kako to onaji yō ni settei shite kudasai.
Please have settings be like they were in the past.
22. 猿たちはいつもと同じように遊んでいます。
Sarutachi wa itsu mo to onaji yō ni asonde imasu.
The monkeys are playing like they always do.
Adverbial Form: A + Onajiku 同じく + B
The form onajiku 同じく is reminiscent of when it was more like a regular adjective. In typical speech and writing, it isn't used that much, but when it is used, its meaning is most similar to "ditto" and "same as."
23. 彼と同じく私もイギリス出身です。
Kare to onajiku watashi mo igirisu shusshin desu.
Ditto to him, I too am from England.
24. 昨日と同じく今日も雨だ。
Kinō to onajiku kyō mo ame da.
Same as yesterday, today is also rain.
25a. 軌を同じくする。
Ki wo onajiku suru.
25b. 軌を一にする
Ki wo itsu ni suru.
To have the same way of doing.
26a. 志を同じくする。
Kokorozashi wo onajiku suru.
26b. 他人と同じように感じる。
Tanin to onaji yō ni kanjiru.
To be like-minded.
Adverbial Form: Onaji 同じ
When used in conjunction with the particle nara なら, which creates “if” statements when making suggestions, onaji 同じ becomes an adverb meaning “anyhow” and is interchangeable with dōse どうせ.
27. 同じ買うなら、地元で買った方がいい。
Onaji kau nara, jimoto de katta hō ga ii.
Anyhow, if you’re going to buy, it’s best to buy local.
Grammar Note: Verb + -ta hō ga ii た方がいい is a grammatical pattern meaning “it’s best to…”
28. 同じ売るなら、少しでも得したい。
Onaji uru nara, sukoshi demo toku shitai.
Anyhow, if I'm going to sell it, I want to get at least some profit.
Grammar Note: Verb + -tai (to omou) たい（と思う）is a grammatical pattern meaning “want to…”
29. 同じお金がかかるなら、自分の家を建てたいと思う。
Onaji okane ga kakaru nara, jibun no ie wo tatetai to omou.
Anyhow, if it's going to cost money, I’d want to build my own house.
Dō- 同
You will also discover a lot of words that start with the character 同 when read as dō in Sino-Japanese compounds. Most of these words are literary, but this is not always the case. For example, the word for sympathy is dōjō 同情, which is simply the characters for “same” and “emotion” put together.
30. 上記、利用規約に同意します。
Jōki, riyō kiyaku ni dōi shimasu.
You agree to the above user agreement.
31. 由香里さんの彼氏と私の夫は同一人物に違いありません！
Yukari-san no kareshi to watashi no otto wa doitsu jimbutsu ni chigai arimasen!
Yukari’s boyfriend and my husband are no doubt the exact same individual!
32. 前回と同様に実験を開始しました。
Zenkai to dōyō ni jikken wo kaishi shimashita.
We began the experiment similarly to last time.
33. 英語の同音異義語を教えてください。
Eigo no dō’on igigo wo oshiete kudasai.
Please teach me English homophones.
34. 看護師は医者と同等ですか。
Kangoshi wa isha to dōtō desu ka?
Are nurses equivalent to doctors?
35. 被災者に同情します。
Hisaisha ni dōjō shimasu.
I sympathize with disaster victims.
36. 東南アジアの国々も隣国同士は仲が悪いですか。
Tōnan ajia no kuniguni mo ringoku dōshi wa naka ga warui desu ka?
Why is it that neighboring countries among Southeast Asian nations have such bad relations?
37. 同志よ、行くぞ。
Dōshi yo, iku zo!
Comrades, let’s go!
Phrase Note: In Mandarin Chinese, 同志 means "homosexual." However, in Japanese, it is a somewhat uncommon word meaning “comrade.”
38. 私は同性と付き合っています。
Watashi wa dōsei to tsukiatte imasu.
I’m dating someone of the same sex.
39. 私も全く同感です。
Watashi mo mattaku dōkan desu.
I completely agree/feel exactly the same way.
40. 外国人の同僚と喧嘩になった。
Gaikokujin no dōryō to kenka ni natta.
I got into an argument with a foreign colleague.