Learn Hardcore Japanese: watasi ha tukue no ue wo kirei ni katadukemasu.

は marks the topic of the sentence: what we are talking about. In this sentence, 私 is just setting the topic “as for me…” and the rest says what I do.

If you used 私が机の上をきれいに片付けます, it would sound like you are emphasizing I (as opposed to someone else) am the one who cleans it.

So:

私は机の上をきれいに片付けます。 = Speaking about me, I tidy the top of the desk.
私が机の上をきれいに片付けます。 = I (not others) am the one who will tidy the top of the desk.

Can I leave out 私 in this sentence?

Yes. In natural Japanese, subjects like 私 are often omitted when they are obvious from context.

So in a normal conversation, you would very often just say:

机の上をきれいに片付けます。
or, in casual speech:
机の上をきれいに片付ける。

Listeners will assume “I” from context, so you don’t need to say 私 unless you want to contrast yourself with someone else or avoid ambiguity.

What does 机の上 literally mean, and how is it put together?

机の上 is built as noun + の + noun:

机 = desk
上 = top, surface, “on” (as a noun)
机の上 = the top/surface of the desk

So literally it is “the desk’s top”, which we naturally translate as “on (top of) the desk” in English.

Why is を attached to 机の上? What is the direct object here?

In 机の上をきれいに片付けます, the thing being tidied (the direct object) is 机の上 – the surface of the desk.

Think of it as “I tidy the area that is the top of the desk.” The whole phrase 机の上 acts as one noun, so を marks it as the direct object of 片付けます.

Grammatically, it parallels English:

机の上を片付ける ≈ “to tidy (up) the top of the desk.”

Why not say 机の上に instead of 机の上を here?

に usually marks a destination / target (go to somewhere, put something on/into somewhere) or a point in time, while を marks the direct object (the thing affected by the action).

Compare:

机の上を片付ける
– The desk top is what you clean / clear.
– You remove things from that area.
机の上に本を置く
– The desk top is where you put the book (target location), so に is used.

If you said 机の上に片付ける, it would mean “to put things away onto the desk”, which is the opposite of cleaning it up. That’s why を is correct in your sentence.

Why is きれい followed by に? What grammar is that?

きれい is a na-adjective. Na-adjectives typically become adverbs by adding に.

So:

きれい（な）部屋 = a clean / neat room (adjective)
きれいに片付ける = to tidy neatly / cleanly (adverb)

In this sentence, きれいに modifies 片付けます, describing how you tidy. You cannot say ✗ きれい片付けます; you need きれいに片付けます.

Is きれい an adjective or a noun? What kind of adjective is it?

きれい is primarily a na-adjective (形容動詞). It behaves differently from typical i-adjectives like 大きい or 小さい.

Before a noun: きれいな机 (a clean / neat desk)
As a predicate: 机はきれいだ / きれいです (the desk is clean)
As an adverb: きれいに片付ける (to tidy neatly / cleanly)

It can also function as a noun meaning something like “cleanliness / beauty”, but in this sentence it is an adjective used adverbially with に.

What is the nuance of 片付けます compared with 掃除します?

Both relate to cleaning, but their focus is different:

片付けます (片付ける)
- To put things away, clear up, tidy.
- Focus: organizing, removing clutter, putting items back in place.
掃除します (掃除する)
- To clean in the sense of removing dirt/dust (sweeping, vacuuming, wiping).
- Focus: making something physically clean, not just organized.

So:

机の上を片付けます = I clear and tidy the top of the desk (put things away).
机の上を掃除します = I clean the top of the desk (wipe it, remove dust).

You can of course do both in real life, but the verbs highlight different aspects.

What tense is 片付けます? Can it mean both “clean up” and “will clean up”?

片付けます is the polite non-past form. Japanese non-past covers both present/habitual and future meanings.

So 片付けます can mean:

“I tidy (regularly)” – habitual:
- 毎朝、机の上をきれいに片付けます。
  – I tidy the top of the desk every morning.
“I will tidy” – future intention:
- 後で机の上をきれいに片付けます。
  – I will tidy the top of the desk later.

Past is 片付けました (“cleaned up”), and dictionary/plain form is 片付ける.

Can the word order change? For example, is 私はきれいに机の上を片付けます correct?

Yes. Japanese word order is quite flexible as long as the verbs and particles stay attached to their words.

All of these are grammatically acceptable:

私は机の上をきれいに片付けます。 (most natural)
私はきれいに机の上を片付けます。 (also fine)
机の上を私はきれいに片付けます。 (emphasizes 机の上 a bit)

The default, neutral order is usually [topic] は [object] を [adverb] [verb], which is what your original sentence uses. Putting きれいに right before the verb is very common and sounds natural.

Is there a difference between 机を片付けます and 机の上を片付けます?

Yes, the nuance changes.

机の上を片付けます。
- You tidy the surface / top of the desk (clear books, papers, etc.).
- This is what you normally say when you clean up the clutter on your desk.
机を片付けます。
- Literally “I tidy the desk.”
- This can mean you move / put away / remove the desk itself, or more generally deal with the desk as an object.
- Context can sometimes make it mean “tidy the desk (area)” but 机の上を片付けます is much clearer for “tidy the top of the desk.”

How would this sentence look in casual speech? What are some natural variations?

In casual conversation, you normally drop 私 and the polite ます ending:

机の上をきれいに片付ける。

Some very natural variations you might hear:

机の上、きれいに片付けるね。 – I’ll tidy the top of the desk, okay.
机の上、ちゃんと片付けて。 – Tidy the top of the desk properly, please.
机の上をきれいにしとくよ。 – I’ll make sure the top of the desk is clean/neat.

The core grammar (particles の, を, に, and the verb 片付ける) stays the same; mainly the politeness and some wording change.