Learn Hardcore Japanese: kyou ha itiniti uti de sizuka ni nihongo wo benkyousuru tumori desu. - I plan to study Japanese quietly at home all day today.

You could say 今日 with に in other sentences (e.g. 今日にします “I’ll make it today”), but when you’re just saying what you’re going to do today, it’s very natural to treat “today” as the topic and use は:

今日は一日うちで… = “As for today, (I will…)”

So here, は is not a time marker; it’s a topic marker, introducing “today” as the theme of the sentence.

What does 一日 do here, and why is there no particle after it?

一日 (いちにち) here means “for the whole day / all day long.”

Japanese often omits a particle after duration expressions, especially with common patterns like:

一日うちで〜
一週間日本にいました
三時間勉強しました

So:

一日うちで〜 ≈ “(spending) the whole day at home (doing…)”

You could add 中 and say 一日中うちで…, which emphasizes “all day long” even more strongly, but 一日 alone is already very natural.

What’s the difference between うち and いえ / 家? Why use うち here?

Both can refer to “home/house,” but the nuance differs:

うち
- Very common in conversation
- Often feels like “my place / our home”
- Has a slightly more personal, warm nuance
いえ / 家
- More neutral word for “house, home, building”
- Can sound a bit more formal or just less “personal” than うち in casual speech

In “stay at home, study at home” contexts, うち is extremely natural.
一日家で静かに日本語を勉強するつもりです is not wrong, but うちで feels more like “at home (my place).”

Why is it うちで and not うちに?

で marks the place where an action happens; に often marks a destination or endpoint.

うちで勉強する = study at home (place where the action occurs)
うちに帰る = go home (to home as a destination)

Since 勉強する is an action performed at a location, で is the correct particle.

Why is it 静かに and not 静か?

静か is a な-adjective (“quiet”), and to make it into an adverb (“quietly”), you change it to 静かに.

静かな部屋 = a quiet room
静かに勉強する = to study quietly

So 静かに is modifying 勉強する: “to study quietly.” Leaving it as 静か would be ungrammatical in this position.

How does 静かに grammatically function in the sentence?

静かに is the adverbial form of the な-adjective 静か, and it modifies the verb 勉強する.

So the core structure is:

静かに勉強する = “study quietly”

It does not modify 日本語; it describes how the studying is done. The full idea is “(I will) quietly study Japanese.”

Why is it 日本語を instead of 日本語で?

Here, 日本語 is the object of the verb 勉強する, so it takes を:

日本語を勉強する = study Japanese

If you use 日本語で, that usually means “by means of Japanese / in Japanese,” indicating the language used to perform some other action:

日本語で話す = speak in Japanese
日本語で書く = write in Japanese

In this sentence, you are studying Japanese itself, so を is correct.

What’s the nuance of 勉強するつもりです compared to 勉強します?

Both can describe a future action, but:

勉強します
- Simple, neutral statement of intention or scheduled action
- “I will study / I study”
勉強するつもりです
- Literally “I intend to study”
- Emphasizes your personal intention or plan
- Implies you have (consciously) decided to do it

In English terms, 勉強するつもりです is closer to “I’m planning to study / I intend to study,” while 勉強します is more like a plain “I will study.”

Why is it 勉強するつもりです and not 勉強しますつもりです?

The pattern with つもりだ / つもりです is:

[dictionary-form verb] + つもりだ / です

So you must use the plain dictionary form:

勉強するつもりです (correct)
勉強しますつもりです (incorrect)

Other examples:

行くつもりです (not 行きますつもりです)
食べるつもりです (not 食べますつもりです)

Can I drop 私は at the beginning? How do people usually say this?

Yes. In Japanese, the subject 私 (I) is often omitted when it’s obvious from context.

（私は）今日は一日うちで静かに日本語を勉強するつもりです。

This is completely natural. In everyday speech and writing, most speakers would drop 私は here.

How would this sentence look in casual (plain) speech?

The main change is at the end: です → だ (or omitted in some styles).

Natural casual versions:

今日は一日うちで静かに日本語を勉強するつもりだ。
With friends, you might even say:
- 今日は一日うちで静かに日本語勉強するつもり。 (dropping を in casual speech)

The meaning stays the same; only politeness level changes.

What’s the difference between 〜つもりです and 〜予定です?

Both can be translated as “plan to ~,” but their nuance is different:

〜つもりです
- Focus on your intention/decision
- Internal, personal plan
- “I intend to / I’m thinking of ~”
〜予定です
- More like a scheduled plan
- Often used for fixed plans, timetables, appointments
- “It is scheduled / I’m scheduled / I have it planned”

In this sentence:

勉強するつもりです = “I intend to study (I’ve decided I’ll do it)”
勉強する予定です = “I’m scheduled / planning to study (it’s on my schedule)”

Both are possible, but つもり feels more like a personal intention.

Can I change the word order, like moving 一日 or 静かに around?

Japanese word order is relatively flexible as long as you keep the verb at the end and the particles with their words. These are all acceptable:

今日は一日うちで静かに日本語を勉強するつもりです。
今日は一日うちで日本語を静かに勉強するつもりです。
今日はうちで一日静かに日本語を勉強するつもりです。

The nuance can shift slightly (what you want to emphasize), but all are grammatically fine.

What you cannot do is break the particle connections, e.g. separating 日本語 from を, or putting the verb somewhere other than (near) the end.

Why do we use に to make 静か into 静かに, but for adjectives like 早い we use 早く (not 早いに)?

Because 静か is a な-adjective, and 早い is an い-adjective. Their adverb forms are made differently:

な-adjectives: 静か → 静かに
- 静かに話す = speak quietly
い-adjectives: 早い → 早く
- 早く起きる = get up early

So:

静かに勉強する (correct)
早く勉強する (correct)

Each adjective type has its own standard way to form an adverb.