hon ga oosugite, kono heya ha sukosi semai desu.

Because 多い and 多すぎる do not take a direct object with を.

In Japanese, 本が多い literally works like books are many or there are many books. The books are the thing being described as numerous, so they are marked with が.

• 本が多い = There are many books.
• 人が多い = There are many people.

Using を would sound wrong here because 多い is not an action done to books.

多すぎて is made from:

• 多い = many / numerous
• すぎる = to exceed / to be too much
• て = a connecting form

So 多すぎて means being too many... or because there are too many...

In this sentence, it connects the first idea to the second:

• 本が多すぎて、 = Because there are too many books...
• この部屋は少し狭いです。 = this room is a little cramped/small.

So 〜すぎて often gives a cause or result.

Here, は marks この部屋 as the topic of the main statement.

The sentence is structured like this:

• 本が多すぎて、 = Because there are too many books,
• この部屋は少し狭いです。 = as for this room, it is a little cramped.

Using は makes this room the thing you are commenting on.

If you used が instead, it would put stronger focus on this room itself as the subject, which would change the nuance a little. For a basic descriptive sentence like this, は is very natural.

少し is an adverb here, meaning a little or slightly, and adverbs usually come before the word they modify.

So:

• 少し狭い = a little narrow / a little cramped

This is very common in Japanese:

• 少し高い = a little expensive
• 少し難しい = a little difficult

It softens the statement, just like a little or slightly in English.

Because 狭い is an い-adjective.

With い-adjectives, the polite form is simply:

• 狭いです

You do not add だ after an い-adjective.

Compare:

• 静かだ / 静かです → 静か is a な-adjective
• 狭い / 狭いです → 狭い is an い-adjective

So:

• 狭い = plain
• 狭いです = polite

Yes, that is completely normal.

In Japanese, when clauses are connected, politeness is usually shown in the final predicate, not in every part of the sentence.

So this is natural:

• 本が多すぎて、この部屋は少し狭いです。

The first clause uses the normal connective form 多すぎて, and the final clause carries the politeness with です.

This pattern is extremely common:

• 忙しくて、行けません。 = I’m busy, so I can’t go.
• お金がなくて、大変です。 = I have no money, so it’s hard.

Not exactly. 狭い more literally means narrow, cramped, or not spacious.

For a room, English often translates it as small, but the nuance is closer to:

• cramped
• tight
• not roomy enough

So in this sentence, the idea is probably not that the room’s physical size changed, but that it feels cramped because there are too many books.

Yes.

You could say:

• 本が多すぎるので、この部屋は少し狭いです。
• 本が多すぎるから、この部屋は少し狭いです。

These also mean because there are too many books, this room is a little cramped.

Nuance:

• 〜て often sounds smooth and natural when linking cause and result.
• ので can sound a bit softer or more explanatory.
• から can sound a bit more direct.

All are possible, but 〜て is very common in everyday Japanese.

Japanese often describes situations differently from English.

English commonly says:

• I have too many books.

Japanese often focuses on what exists or what the situation is:

• 本が多い = There are many books.
• 本が多すぎる = There are too many books.

If you want to say I have too many books, you could say something more personal, such as:

• 私は本をたくさん持っています。 = I have a lot of books.

But in this sentence, the focus is on the state of the room, so 本が多すぎて fits very well.

To some extent, yes. Japanese word order is more flexible than English, as long as the particles make the roles clear.

The original sentence:

• 本が多すぎて、この部屋は少し狭いです。

is very natural because it gives the cause first and the result second.

A different order like:

• この部屋は、本が多すぎて、少し狭いです。

is also understandable, but it sounds a little different in rhythm and focus. Learners should usually stick with the original pattern:

cause/result clause + main statement

because it is clear and natural.

The comma simply marks a pause between the two parts of the sentence.

• 本が多すぎて、 = because there are too many books,
• この部屋は少し狭いです。 = this room is a little cramped.

Japanese punctuation is somewhat flexible, so the sentence could also be written without the comma:

• 本が多すぎてこの部屋は少し狭いです。

Both are fine, but the comma makes it easier to read.