Learn Hardcore Japanese: hurui beddo wo utte, isu mo bunbougu mo kirei ni narabemasita. - I sold my old bed and neatly arranged my chair and stationery.

Grammatically, the comma is optional; the て‑form already connects the actions. The comma just makes the structure easier to read, similar to writing in English:

“I sold the old bed, and then I neatly arranged the chairs and stationery.”

What does the も … も construction mean with 椅子も文房具も?

When も is used twice like AもBも, it often means “both A and B”.

So:

椅子も文房具もきれいに並べました。
→ “I neatly arranged both the chairs and the stationery.”

Key points:

AもBも = both A and B (all of them are included).
This is different from a single も, which usually means “also / too.”

Why is も used instead of を after 椅子 and 文房具?

The main function here is to show “both A and B”, so も is used to add that inclusive nuance.

Technically, the direct object marker を is omitted:

Full, slightly heavier version:
椅子も文房具もをきれいに並べました。
Natural spoken/written Japanese:
椅子も文房具もきれいに並べました。

In this sentence:

も marks 椅子 and 文房具 as the items involved,
and the role of “object of 並べました” is understood from context, so を is dropped.

What does きれいに do here, and why is it に and not something like きれいだ?

きれい is a な‑adjective. To turn a な‑adjective into an adverb (something that modifies a verb), you change 〜だ / な to 〜に.

きれいだ = is pretty / clean (adjectival, describes a noun or state)
きれいに = neatly, cleanly (adverb, describes how an action is done)

So:

きれいに並べました = “arranged [them] neatly / in an orderly way.”

You cannot say きれいだ並べました; you need the adverbial form きれいに.

What is the nuance difference between きれい as “pretty” and as “neat / clean” here?

きれい has multiple common meanings:

visually beautiful / pretty
clean
neat / orderly / well‑arranged

In きれいに並べました, the third meaning is most natural:

It does not mean “made the chairs and stationery beautiful,”
but “arranged them neatly / in an orderly way.”

Context (we are arranging furniture and stationery) guides you to the “neat, orderly” meaning.

What is the difference between 並べました and 並びました? Why is 並べました used?

Japanese has many transitive / intransitive verb pairs. Here:

並べる (transitive): to line up / arrange something
並ぶ (intransitive): to line up / something lines up (by itself or people do it themselves)

In this sentence, the speaker is actively arranging items:

椅子も文房具もきれいに並べました。
→ “I arranged the chairs and stationery neatly.”

So the transitive verb 並べる is needed.
並びました would mean “(they) lined up,” implying the chairs and stationery arranged themselves, which is not the intended meaning.

Where is the subject in this sentence? Who is doing the actions?

The subject is omitted, which is very common in Japanese when it is obvious from context.

Grammatically, the sentence is something like:

(私は) 古いベッドを売って、椅子も文房具もきれいに並べました。
→ “(I) sold the old bed and neatly arranged the chairs and stationery.”

Depending on context, the subject could be I, we, he, she, etc. Japanese does not need to state it if everyone already knows who is acting.

Why is ベッド in katakana, but 椅子 and 文房具 are in kanji?

This reflects typical Japanese writing conventions:

ベッド is a loanword from English (“bed”), so it is written in katakana, the script usually used for loanwords and some onomatopoeia.
椅子 and 文房具 are native / Sino‑Japanese words with established kanji:
- 椅子 = chair
- 文房具 = stationery

So the different scripts are not a grammatical difference, just normal spelling conventions.

Could the sentence be written without spaces between the Japanese words?

Yes. Standard Japanese writing does not normally use spaces between words. The sentence would usually appear as:

古いベッドを売って、椅子も文房具もきれいに並べました。

The spaces in your version are probably there to help learners see the word boundaries. The meaning and grammar are the same with or without spaces.