tukue no ue ni hokori ga atta node, nureta taoru de hukimasita.

机の上 literally means the top/surface of the desk.

• 机 = desk
• 上 = ऊपर / top / above
• の links the two nouns, so 机の上 = the desk’s top / on the desk

Then に marks the location where something exists.

So:

• 机の上に = on the desk

Why not the others?

• 机に上 is ungrammatical.
• 机上 is a real word, but it is more formal/literary and often used in expressions like 机上の空論. In everyday speech, 机の上 is much more natural.

Here, に marks the place where something exists.

The verb ある means to exist / to be present for inanimate things. With ある, the location is usually marked by に.

So:

• 机の上にほこりがあった
• There was dust on the desk

A useful pattern is:

• 場所 に 物 が ある
• Something is in/at/on a place

Examples:

• 部屋に椅子がある = There is a chair in the room.
• テーブルの上に本がある = There is a book on the table.

が marks ほこり as the thing that existed.

In this sentence, the speaker is introducing or pointing out the dust as the relevant thing present on the desk:

• ほこりがあった = there was dust

Using は would change the nuance. It could sound more contrastive, like:

• ほこりはあった = there was dust, at least... / as for dust, there was some

That might make sense in a context where you are contrasting dust with something else, but here が is the natural choice.

あった is the past plain form of ある.

• ある = to exist / to be (for inanimate things)
• あった = existed / was there

Because ほこり is an inanimate thing, Japanese uses ある, not いる.

So:

• ほこりがあった = there was dust

If it were a person or animal, you would normally use いる instead:

• 猫がいた = There was a cat.

This is very common in Japanese.

In many sentences, the final verb carries the overall politeness, while earlier clauses often stay in plain form, especially before connectors like ので.

So:

• ほこりがあったので、拭きました。

is perfectly natural.

You could also hear a more uniformly polite version:

• ほこりがありましたので、拭きました。

That sounds more formal. In everyday polite speech, the mixed pattern in your sentence is normal and natural.

ので means because / since, and it gives the reason for the action in the main clause.

So:

• ほこりがあったので、ぬれたタオルで拭きました。
• Because there was dust on the desk, I wiped it with a wet towel.

Difference from から:

• から is also because
• ので often sounds a little softer, more explanatory, and slightly less direct
• から can sound more assertive

Compare:

• ほこりがあったので、拭きました。 = Because there was dust, I wiped it.
• ほこりがあったから、拭きました。 = Because there was dust, I wiped it.

Both are correct. ので often feels a bit more neutral or gentle.

Yes, ぬれた is the past form of ぬれる (to get wet), but when it modifies a noun, it often works like an adjective in English.

So:

• ぬれたタオル = a wet towel

This does not necessarily emphasize past time in English. It just describes the towel as being in a wet state.

Japanese often uses verb forms before nouns this way:

• 割れたガラス = broken glass
• 閉まったドア = a closed door
• ぬれた服 = wet clothes

So even though it is grammatically a past form, the natural translation here is simply wet towel, not towel that got wet unless the context specifically emphasizes that.

Here, で marks the tool or means used to do the action.

So:

• ぬれたタオルで拭きました
• I wiped it with a wet towel

This is a very common use of で:

• 箸で食べる = eat with chopsticks
• ペンで書く = write with a pen
• スポンジで洗う = wash with a sponge

So in this sentence, で means with / using.

The object is omitted because it is understood from context.

拭く means to wipe. In English, you usually need to say what was wiped, but Japanese often leaves it out if it is obvious.

From the previous clause, the listener can infer that the speaker wiped:

• the dust
• the top of the desk
• or the dusty area on the desk

A fuller version could be:

• 机の上をぬれたタオルで拭きました。 = I wiped the top of the desk with a wet towel.
• ほこりをぬれたタオルで拭きました。 = I wiped away the dust with a wet towel.

Your sentence leaves that unsaid because Japanese often omits obvious information.

Because the sentence does not explicitly say what was wiped.

If the speaker wanted to say I wiped the top of the desk, then を would appear:

• 机の上を拭きました。

If the speaker wanted to say I wiped the dust, then:

• ほこりを拭きました。

But instead, the sentence simply says:

• ぬれたタオルで拭きました。
• (I) wiped (it) with a wet towel.

The object is omitted because it is clear enough from context.

In this sentence, it means on.

That is because 机の上 means the top surface of the desk, and dust naturally exists on that surface.

So:

• 机の上にほこりがあった = There was dust on the desk.

In other contexts, 上 can also mean above, depending on what kind of noun phrase and situation you have. But with 机の上, the usual everyday meaning is on top of the desk.

Yes.

• 机の上にほこりがありましたので、ぬれたタオルで拭きました。

This is more uniformly polite and a bit more formal.

Your original sentence:

• 机の上にほこりがあったので、ぬれたタオルで拭きました。

is also natural and very common in polite conversation. Japanese often uses a plain form in a subordinate clause and a polite form at the end.

So both work, but the nuance is slightly different:

• あったので = natural everyday style
• ありましたので = more formal/polite

No. Normal Japanese writing usually does not use spaces between words.

So this sentence would normally be written as:

机の上にほこりがあったので、ぬれたタオルで拭きました。

The spaces are often added in learning materials to make the structure easier to see.

Yes, it is natural.

A ぬれたタオル is simply a wet/damp towel.

Depending on context, Japanese might also use expressions like:

• 湿ったタオル = a damp/moist towel
• 濡れたタオル = same as ぬれたタオル, but with kanji

In everyday speech and basic learning contexts, ぬれたタオル is a very natural and easy expression.

A simple breakdown is:

• 机の上に = on the desk
• ほこりがあったので = because there was dust
• ぬれたタオルで = with a wet towel
• 拭きました = (I) wiped

So the structure is:

[place] に [thing] があったので、[tool] で [action]

Or more generally:

Because X existed/was there, I did Y using Z.

This is a very useful pattern for building your own sentences.