Learn Hardcore Japanese: kyuukei no aida ni nihongo no tango wo oboemasu. - During the break, I memorize Japanese words.

の here is the general “linking” particle between two nouns. It often corresponds to “of” or “’s” in English, but not always in a literal possessive sense.

休憩の間
Literally: the interval/period of the break → “during the break” / “the time while on break”
Here 休憩 (break) is specifying what kind of 間 (interval/period) it is.
日本語の単語
Literally: words of the Japanese language → “Japanese vocabulary words”
日本語 (Japanese language) specifies what kind of 単語 (words/vocabulary items) they are.

So A の B here is “B that is related to A / B of A / A-type B,” not ownership like “A owns B.”

What does 間 mean in this sentence, and how is 間 different from 間に?

間 (あいだ) basically means “interval” / “period (of time)” or “space between.”

休憩の間 → the time of the break / the duration of the break
When you add に → 休憩の間に → in/within the period of the break ⇒ “during the break.”

Difference:

間 on its own just names the span of time.
間に adds the particle に, which marks a time frame in/within which something happens.

So [time] に [action] = the action happens at / during / within that time.
Here: 休憩の間に覚えます = “(I) memorize (them) during the break.”

Could I say 休憩中に日本語の単語を覚えます instead? What’s the difference between 休憩の間に and 休憩中に?

Yes, 休憩中に日本語の単語を覚えます is natural and correct.

Nuance:

休憩の間に
- Focuses on the entire period of the break.
- Means “sometime during the break” or “while the break lasts.”
- Slightly more neutral/general.
休憩中に
- 中 (ちゅう) emphasizes the state of being in the middle of something.
- Sounds more like “while (I’m) in the middle of my break” / “during break time (while it’s going on).”

In many casual contexts they overlap in meaning and both can be used. Learners can usually treat them as near-synonyms here.

Why is there no subject like 私 in the sentence? How do we know it means “I (will) memorize…”?

In Japanese, the subject is often omitted when it’s clear from context.

English requires something like “I,” “you,” “we,” etc.
Japanese usually drops pronouns if everyone already knows who is doing the action.

In a typical conversation:

If you are talking about your own study habits, context makes it obvious that you are the one memorizing.
So 休憩の間に日本語の単語を覚えます is naturally interpreted as “I (will) memorize Japanese vocabulary during the break.”

If you really want to include it:

私は休憩の間に日本語の単語を覚えます。
But including 私 all the time can sound unnatural or overly emphatic.

What exactly does 覚えます mean here? How is 覚える different from 勉強する?

覚える (おぼえる) means:

to memorize
to learn and retain
to come to remember something

So 単語を覚えます = “I will memorize words / I will commit the words to memory.”

勉強する (べんきょうする) means:

to study (in a broad sense: reading, doing exercises, etc.)

Compare:

日本語の単語を勉強します。
→ “I study Japanese vocabulary.” (maybe reading, practicing, reviewing)
日本語の単語を覚えます。
→ “I (set out to) memorize Japanese vocabulary (so that I will remember them).”

In this sentence, 覚えます emphasizes the goal of actually memorizing the vocab, not just studying it in general.

The verb is 覚えます, which looks like present tense. Does this mean “I memorize” (habit) or “I will memorize” (future)?

Japanese non-past form (-ます / dictionary form) covers both:

present / habitual actions
future / planned actions

So 覚えます can mean:

“I memorize (as a habit)”
“I will memorize” / “I’m going to memorize” (future plan or intention)

Which one it is depends on context:

Talking about your routine:
→ “During the break, I memorize Japanese vocabulary.” (habit)
Talking about what you plan to do next break:
→ “During the break, I will memorize Japanese vocabulary.”

Japanese does not have a dedicated future tense like English; context resolves it.

Why is the particle に used in 休憩の間に and not で?

Both に and で can relate to time, but they have different roles.

に after a time expression usually marks a point or period in/within which something happens.
- 休憩の間に覚えます。
  → The memorizing happens during the break.
で is mainly used for:
- location of an action (学校で勉強します – “I study at school”)
- means / method (バスで行きます – “I go by bus”)
- certain time-limit expressions (e.g., １時間で終わります – “I’ll finish in one hour” = within that span, as a limit)

For “during the break” in the sense of within that time period, に is the natural choice: 休憩の間に.

Why do we use を with 単語? What does 単語を覚えます literally say?

を marks the direct object of the verb: the thing that the action is directly done to.

単語 = vocabulary word(s)
覚えます = (I) memorize / learn (and retain)
単語を覚えます = “(I) memorize words.”

Literally: “(I) do the action of memorizing to the words.”
So X を覚えます = “memorize X.”

That’s why 単語 takes を here.

Can I change the word order to 日本語の単語を休憩の間に覚えます? Is that still correct?

Yes, that sentence is also grammatical and natural.

Japanese word order is relatively flexible as long as:

particles stay attached to the correct word, and
the verb typically comes at the end.

Both are fine:

休憩の間に日本語の単語を覚えます。
日本語の単語を休憩の間に覚えます。

The nuance is only about slight emphasis:

Putting 休憩の間に closer to the start may slightly highlight “during the break”.
Putting 日本語の単語を first may slightly highlight “Japanese vocabulary” as what you’re dealing with.

But in ordinary speech both sound natural, and the difference is minor.

Why 単語 and not 言葉 or other words for “word” or “vocabulary”?

Several Japanese words relate to “words” or “vocabulary,” with different nuances:

単語 (たんご)
- Individual vocabulary items, especially in a study/learning context.
- Like English “vocabulary words” in a textbook or word list.
言葉 (ことば)
- More general “word(s), expression(s), language, speech”.
- Often used for phrases, expressions, or language in a broader, more natural sense.

In a study context, where you deliberately memorize vocab items, 単語 is the most natural choice:

日本語の単語を覚えます。
→ “I memorize Japanese vocabulary (entries).”

You could say 日本語の言葉, but it sounds less like a textbook/flashcard type of vocab list and more like “Japanese words/phrases” in a broader sense.

Why isn’t it 日本語単語 without の? In English we often say “Japanese words” with no “of”.

Japanese usually puts の between two separate nouns when one modifies the other:

日本語の単語
→ literally “Japanese-language words”

There are compound nouns where の drops (like 英和辞典 – “English-Japanese dictionary”), but:

日本語単語 is not a common compound as-is.
Native speakers would naturally say 日本語の単語.

So in this case, の is necessary and natural. English “Japanese words” corresponds to Japanese 日本語の単語, not 日本語単語.

How would I say the negative or past forms of this sentence?

Starting from:

休憩の間に日本語の単語を覚えます。
→ non-past, polite

You can change 覚えます:

Negative (polite):
- 休憩の間に日本語の単語を覚えません。
  → “I do not memorize / I will not memorize Japanese vocabulary during the break.”
Past (polite):
- 休憩の間に日本語の単語を覚えました。
  → “I memorized Japanese vocabulary during the break.”
Past negative (polite):
- 休憩の間に日本語の単語を覚えませんでした。
  → “I did not memorize Japanese vocabulary during the break.”

The rest of the sentence stays the same; only the verb ending changes.