Learn Hardcore Japanese: heya ni atarasii isu to beddo wo okitai desu. - I want to put a new chair and bed in my room.

In 部屋に新しい椅子とベッドを置きたいです, the important point is where the chair and bed will end up, so 部屋に is correct.
部屋で椅子とベッドを置きたいです sounds wrong, because we are not describing “doing the action in the room” in that sense; we’re describing “placing them into the room as the destination.”

What exactly does 置きたい mean here, and why use 置く instead of other verbs like ある, 入れる, or 欲しい?

置く means “to put / place / set (something somewhere) and leave it there for a while.”
So 置きたい = “want to put/place (and leave there).”

部屋に新しい椅子とベッドを置きたいです。
= I want to put/place a new chair and bed in the room.

Contrast with:

部屋に新しい椅子とベッドが欲しいです。
= I want (there to be) a new chair and bed in the room / I want a new chair and bed for the room.
→ Focuses on wanting the items, not on the action of placing them.
部屋に椅子とベッドを入れたいです。
= I want to put (bring) a chair and bed into the room.
→ 入れる is “to put into / bring into,” often into a container or inside space; for furniture, 置く is more natural to mean “set it there as furniture.”
ある means “to exist / there is,” so it describes a state, not an action of putting:
- 部屋に椅子とベッドがある。= There is a chair and a bed in the room.

So 置きたい highlights the action/plan of placing the furniture, not just the wish that it exists or that you own it.

How is 置きたい formed from the dictionary form 置く?

The たい-form expresses “want to do (verb).” It’s made from the verb stem + たい.

Take the dictionary form: 置く.
For a godan -く verb, change く to き to get the stem: 置き.
Add たい: 置きたい = “want to put.”

Other examples:

行く → 行き → 行きたい (want to go)
読む → 読み → 読みたい (want to read)
食べる → 食べ → 食べたい (want to eat) — (ichidan verb: drop る to get the stem)

Why do we add です after 置きたい? Isn’t たい already “want to”?

Yes, たい already means “want to,” but 置きたい by itself is in plain (informal) style.

Grammatically, 〜たい behaves like an い-adjective (e.g., うれしい, たかい):

置きたい。= (plain) I want to put…
置きたいです。= (polite) I would like to put…

Adding です makes it polite, just like:

うれしい → うれしいです
たのしい → たのしいです

So 置きたいです is simply the polite way to say “I want to put (them).”

Where is the subject “I” in this sentence? I don’t see 私.

Japanese often omits the subject when it’s obvious from context.

In 部屋に新しい椅子とベッドを置きたいです, nothing explicitly says “I,” but:

〜たい normally expresses the speaker’s own desire (except in questions or quoted speech).

So the default understanding is:

(私は) 部屋に新しい椅子とベッドを置きたいです。
= (I) want to put a new chair and bed in the room.

You can add 私は for clarity or emphasis:

私は部屋に新しい椅子とベッドを置きたいです。
→ “As for me, I want to put …” (contrast with others, etc.)

But in most everyday contexts, it’s naturally omitted.

Why does を appear only after ベッド and not after both 椅子 and ベッド?

In Japanese, when several nouns share the same particle, the particle is usually attached only to the last noun in the list:

映画と音楽が好きです。= I like movies and music.
本とノートとペンを買いました。= I bought a book, a notebook, and a pen.

So:

新しい椅子とベッドを置きたいです。
= I want to put a new chair and bed (object) …

is the normal pattern.

Saying 椅子をとベッドを置きたいです is unnatural and heavy. You normally don’t repeat を in a simple “X and Y” object list.

Does 新しい describe both 椅子 and ベッド, or only the chair?

Grammatically, 新しい椅子とベッド is:

“a new chair and (a) bed.”

The adjective 新しい directly modifies the noun that immediately follows it (椅子). So strictly, only the chair is definitely “new.”

However, in real usage, many people will interpret or allow it to mean both are new, depending on context. It’s a bit ambiguous.

To be clear:

Both are new:
- 部屋に新しい椅子と新しいベッドを置きたいです。
- 部屋に新しい椅子とベッドを両方置きたいです。 (plus some context saying both are new)
Only the chair is new (bed is not):
- 部屋に新しい椅子と古いベッドを置きたいです。

As a learner, if you need to be clear that both are new, it’s safest to repeat the adjective: 新しい椅子と新しいベッド.

Could I say 部屋は新しい椅子とベッドを置きたいです instead of 部屋に? What about 部屋には?

部屋は新しい椅子とベッドを置きたいです。
This is not natural, because 置く still needs a location marked by に.
は is a topic marker, not a location marker, so you can’t replace に with は here.

Correct options:

Keep it as is (no explicit topic):
- 部屋に新しい椅子とベッドを置きたいです。
Make 部屋に the topic by adding は after に:
- 部屋には新しい椅子とベッドを置きたいです。
  → “As for the room, I want to put a new chair and bed (in it).”
  This is natural when you’re contrasting the room with other places (e.g., the living room vs the bedroom).

So pattern:

[Place]に
- [Object]を
  - [Verb] — basic
[Place]には
- [Object]を
  - [Verb] — “As for [place], …” (topic + location)

Can I change the word order, like 新しい椅子とベッドを部屋に置きたいです?

Yes. Because particles show the roles, Japanese word order is somewhat flexible as long as the verb comes last.

These are all grammatically OK:

部屋に新しい椅子とベッドを置きたいです。
新しい椅子とベッドを部屋に置きたいです。

The nuance is subtle:

Starting with 部屋に makes the location feel slightly more foregrounded.
Starting with 新しい椅子とベッドを makes the objects feel slightly more foregrounded.

You cannot normally put the verb in the middle:

✕ 部屋に置きたいです新しい椅子とベッドを
✕ 置きたいです部屋に新しい椅子とベッドを

In normal prose or conversation, keep the main verb at the end.

Why is を used with 置きたい? Could I say 椅子とベッドが置きたいです instead?

With 〜たい, both が and を can appear with the “object” of a transitive verb, but usage varies by verb and context.

For everyday speech:

[Object]を[Verb]たい is the most common, neutral pattern:
- 水を飲みたい。= I want to drink water.
- 本を読みたい。= I want to read a book.
- 椅子とベッドを置きたい。= I want to put a chair and bed.
[Object]が[Verb]たい also exists, often with a feeling of emphasizing “what you want is X”:
- 何が食べたい？= What do you want to eat?
- ケーキが食べたい。= Cake is what I want to eat.

With 置く, 椅子とベッドを置きたいです is the natural, standard choice.
椅子とベッドが置きたいです is possible but feels unusual and would put strong focus on “chair and bed (as opposed to something else) are the things I want to put.”
For learners, you can safely stick to を with 置きたい in this kind of sentence.

Can I use 置きたいです to talk about someone else’s desire, like “Tanaka wants to put a chair and bed in the room”?

Careful: 〜たい normally expresses the speaker’s own desire (or the listener’s, in a question).

For a third person (he/she/they), the usual patterns are:

〜たがっている (is showing signs of wanting to …):
- 田中さんは部屋に新しい椅子とベッドを置きたがっています。
  = Tanaka (apparently) wants to put a new chair and bed in the room.
Or use a quote of what they said:
- 田中さんは部屋に新しい椅子とベッドを置きたいと言っています。
  = Tanaka says (he/she) wants to put a new chair and bed in the room.

You can see sentences like:

田中さんは部屋に新しい椅子とベッドを置きたいです。

but this usually sounds like the speaker is guessing or describing Tanaka’s desire from the outside. For clear, natural Japanese, use 〜たがっています or a quoted 〜たいと言っています for other people’s wants.

What’s the difference between 置きたいです and 置きたいと思います / 置きたいと思っています?

All involve “want to put,” but the nuance differs:

置きたいです。
- Direct statement: “I want to put (them).”
- Simple, straightforward desire now.
置きたいと思います。
- Literally: “I think I want to put (them).”
- Softer / more tentative or polite; often used when making a mild proposal or plan, e.g., at a meeting:
  - 部屋に新しい椅子とベッドを置きたいと思います。
    = I’m thinking I’d like to put a new chair and bed in the room.
置きたいと思っています。
- Literally: “I’ve been thinking that I want to put (them).”
- Suggests an ongoing intention or plan you’ve had for some time, not just a sudden wish.

For a simple learner sentence expressing a straightforward wish, 置きたいです is perfect.