たい(tai) — Expressing Desire

• 日本に行きたいです。

  Nihon ni ikitai desu.

  I want to go to Japan.

  行き (masu-stem of 行く) + たい (want) + です (polite)

• 水が飲みたい。

  Mizu ga nomitai.

  I want to drink water.

  When expressing raw desire, the object particle を often shifts to が (what you want is treated like the subject).

• 今日は何もしたくない。

  Kyou wa nani mo shitakunai.

  I don't want to do anything today.

  したい → したくない: conjugates negatively just like an い-adjective (drop い, add くない).

• ・1st-Person Restriction: たい is normally only for your OWN desires. To talk about what someone ELSE wants, use たがっている (彼は行きたがっています) or quote them (行きたいと言っていました).
• ・Particle Shift: When you want to interact with an object (drink water, eat sushi), を strongly prefers shifting to が. "水を飲みたい" is understood, but "水が飲みたい" is more natural.

Commonly confused with

The JLPT rarely asks whether you recognise a pattern — it asks which of several similar patterns fits. These are the ones たい is tested against.

• てもいい — Giving/Asking Permission
• に行く (ni iku) — Go (in order) To Do
• 天気 — Talking About the Weather
• 家族 — In-Group vs Out-Group Family Terms
• を + 食べる／飲む — Eating and Drinking
• 〜が痛い — Expressing Pain
• だろう／でしょう — Probability & Seeking Agreement
• Set Polite Phrases — Social Lubricants