Once you know たい means "want to do," three questions remain: which particle to use, how to express sustained desire, and how to conjugate it.
The Particle Secret: が vs を
In たい sentences, the object can take either「が」or「を」— different nuance:
| Particle | Emphasis | Example | Nuance |
|---|---|---|---|
| が | Object | 私はビールが買いたい。 | What I want to buy is beer (not something else) |
| を | Action | 私はビールを買いたい。 | I want to buy beer (focus on the action) |
Simply put:
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が = spotlight on "what thing" → Beer!
-
を = spotlight on "what action" → Buy!
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私は水が飲みたい。 → What I want to drink is water. (Not tea, not coffee)
-
私は水を飲みたい。 → I want to drink water. (Focus on the act of drinking)
In daily use both are fine. But on exams, note which emphasis is being tested.
Sustained Desire: たい + と思う
「たい」expresses an immediate impulse. For ongoing, sustained desire, add「と思う」:
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私はこのような車を買いたい。 → I want to buy a car like this. (Right now)
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私はこのような車を買いたいと思っている。 → I've been wanting to buy a car like this. (Ongoing thought)
Why? 「思う」transforms an impulse into a conscious thought — and thoughts can persist.
Conjugation: Same as い-Adjectives
たい conjugates exactly like an い-adjective:
| Form | Example |
|---|---|
| Present affirmative | 食べたい |
| Present negative | 食べたくない |
| Past affirmative | 食べたかった |
| Past negative | 食べたくなかった |
- 私はこのパソコンを使いたかったのに、兄は使わせてくれない。 → I wanted to use this computer, but my brother wouldn't let me.
Note how「使いたかった」is たい past tense, while「使わせてくれない」uses causative — brother won't "let" me. Desire and causative in one sentence — very typical.
Self-Test
Q1. What's the difference between「私は水が飲みたい」and「私は水を飲みたい」?
Show answer
が emphasizes the object: "What I want to drink is water." を emphasizes the action: "I want to drink water." Both correct, different focus.
Q2. How do you turn「この映画を見たい」into sustained desire?
Show answer
この映画を見たいと思っている。 Adding「と思っている」means "I've been wanting to see this movie."
Q3. What's the past negative of「食べたい」?
Show answer
食べたくなかった. Same as い-adjectives: たい → たくない → たくなかった.
Summary
- Particle が emphasizes the object (what you want), を emphasizes the action (what you want to do)
- たい + と思う = sustained desire (from impulse to ongoing thought)
- たい conjugates exactly like い-adjectives: たくない, たかった, たくなかった