itsuka

いつか is one of those Japanese words that looks simple on the surface but hides a surprising amount of nuance. In English, we have “someday” (vague future) and “one day” (either a specific day in the past or an indefinite future day) — and both can translate to いつか. What makes いつか interesting is that the same word works for dreams about the future and memories of the past, and understanding when it applies to each is essential for sounding natural. This guide breaks it all down with clear examples.

Yuka

Hey Rei, what’s the best way to remember the difference between itsuka and (‘it’, ‘that’)?

Rei

The best trick is to associate each word with a strong image or situation. By the end of this article you’ll have one for each — promise!

At a Glance: いつか

いつか Meaning 1: Someday (Vague Future)

The most common use of いつか is to express a wish, hope, or plan for an unspecified point in the future — “someday.” The key nuance is vagueness: you do not know when it will happen, and you are not committing to a specific date. This makes いつか perfect for dreams and aspirations.

Example 1 — a personal dream:

いつか日本語を話せるようになりたい。
Itsuka Nihongo wo hanaseru you ni naritai.
Someday I want to be able to speak Japanese.

Example 2 — travel goal:

いつか京都に行ってみたいです。
Itsuka Kyoto ni itte mitai desu.
Someday I’d like to visit Kyoto.

Example 3 — future hope:

いつかまた会えるといいね。
Itsuka mata aeru to ii ne.
I hope we can meet again someday.

Yuka

That makes sense! So itsuka is about… okay, I think I’m starting to get it.

Rei

You’re getting it! And the more you practice using itsuka in sentences, the more automatic it becomes. Language learning is all about repetition.

いつか Meaning 2: At Some Point (Vague Past)

いつか can also refer to a vague point in the past — “once,” “at some point,” or “one day” in the past-tense sense. This use is less commonly taught but very natural in Japanese. The sentence will use past-tense verb forms to signal that the time frame is the past.

Example 1 — a past memory:

いつかあなたに会ったことがある気がする。
Itsuka anata ni atta koto ga aru ki ga suru.
I have a feeling I met you at some point before.

Example 2 — a past occurrence:

いつかテレビで見たことがある。
Itsuka terebi de mita koto ga aru.
I saw that once on TV at some point.

Example 3 — recalling something from the past:

いつかそんな話を聞いたことがある。
Itsuka sonna hanashi wo kiita koto ga aru.
I remember hearing a story like that once.

Yuka

Alright. And now explain (‘it’, ‘that’)? I want to make sure I have both down.

Rei

Sure! (‘it’, ‘that’) is actually the easier one to remember once you have a clear mental image. Let’s look at the examples.

いつか vs. Related Time Words

いつか is often confused with similar-sounding or similar-meaning time words. Here is how they differ:

Important note: いつか (someday) and 五日 (the 5th of the month) are written differently in kanji but sound identical. Context always makes the meaning clear — if someone says 五月五日 (May 5th), they mean the date, not “someday.”

Using いつか in Sentences — Grammar Notes

いつか is an adverb, which means it modifies the verb and does not need a particle. It typically appears at or near the beginning of a clause.

Decision Flowchart: When to Use いつか

Are you talking about an UNSPECIFIED point in time?
        |
        v
Is it FUTURE (a wish, hope, or plan)?
   |                     |
  YES                    NO (it's in the past)
   |                     |
   v                     v
いつか + want/will     Is it a VAGUE past event
(いつか行きたい)        ("once," "at some point")?
                           |              |
                          YES             NO
                           |              |
                           v              v
                    いつか + past      Use a more specific
                    verb form          time word
                    (いつか見た)       (昨日, 先週, etc.)

Quick Quiz — Test Yourself!

Yuka

Okay Rei, quiz time! I want to test how well I’ve absorbed all this.

Rei

Challenge accepted on your behalf! Let’s see how much of itsuka and (‘it’, ‘that’) has sunk in.

Fill in the blank using いつか and the correct verb form, or identify whether いつか is being used correctly.

Q1. Someday I want to travel around the world.
＿＿＿世界一周したい。
___ sekai isshou shitai.

Answer: いつか
Reason: A future dream with no specific date — exactly what いつか is for.

Q2. I feel like I’ve seen this place somewhere before.
＿＿＿この場所に来たことがある気がする。
___ kono basho ni kita koto ga aru ki ga suru.

Answer: いつか
Reason: A vague past memory — いつか works with past tense to mean “at some point.”

Q3. Someday your hard work will pay off.
＿＿＿努力が報われるよ。
___ doryoku ga mukuwareru yo.

Answer: いつか
Reason: An encouraging statement about an unspecified future moment.

Q4. I saw a movie like that once.
＿＿＿そういう映画を見たことがある。
___ sou iu eiga wo mita koto ga aru.

Answer: いつか
Reason: The ～たことがある pattern combined with いつか naturally expresses a vague past experience.

Q5. We’ll see each other again someday.
＿＿＿またきっと会える。
___ mata kitto aeru.

Answer: いつか
Reason: A hopeful statement about a future meeting at an unspecified time — classic いつか usage.

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