Expressing Desire: 〜たい (Wanting to do / Inner state as adjective)

Mental Model: Turning an Action into an Adjective of Inner State

In English, desire is expressed with the separate verb “to want” (“I want to go”). In Japanese, however, you do not use an auxiliary verb.

Instead, attaching 〜たい fundamentally reclassifies the verb into an い-adjective:

• Wanting to do an action is treated as an internal psychological sensation (akin to feeling hot, cold, or sleepy).
• Just like 寒い(さむい) (“cold”), the compound 行きたい(いきたい) (“wanting to go”) is a complete native predicate.
• When you add です (行きたいです), it is not a grammatical copula—it is purely a polite courtesy cushion tacked on for the listener.

Derivation from the Continuative Stem (連用形)

Drop ます from the polite present stem and attach たい:

• Group 2 (Ichidan / ru-verbs): Drop る and add たい: 食べる(たべる) → 食べます → 食べたい (“want to eat”) · 見る(みる) → 見ます → 見たい (“want to see”) · 起きる(おきる) → 起きたい (“want to wake up”).

• Group 1 (Godan / u-verbs): Shift the final u-vowel to the i-step and add たい: 飲む(のむ) → 飲みます → 飲みたい (“want to drink”) · 行く(いく) → 行きます → 行きたい (“want to go”) · 話す(はなす) → 話します → 話したい (“want to talk”) · 買う(かう) → 買います → 買いたい (“want to buy”).

• Irregular Verbs: する → します → したい (“want to do”) · 来る(くる) → 来ます(きます) → 来たい(きたい) (“want to come”).

The Particle Choice: を vs が

With transitive verbs taking たい, the direct object particle can be either を or が:

• Using が: 水が 飲みたいです。(みずが のみたいです。) Treats 飲みたい as an adjective describing the noun. Highlights the water itself as the object of yearning: “Water is what I crave.” Traditional, natural, and emphasizes the desire.

• Using を: 水を 飲みたいです。(みずを のみたいです。) Treats 飲みたい primarily as an action, keeping the direct object marker を. Emphasizes your active agency: “I want to perform the act of drinking water.”

Both are fully standard today. In casual conversation, を is increasingly common, while が retains a feeling of direct physical craving.

The Four Quadrants of Inflection

Because a たい-verb is now an true い-adjective, it conjugates by dropping い:

• Present Affirmative: 行きたいです(いきたいです) (“I want to go”) · Casual: 行きたい
• Present Negative: 行きたくないです(いきたくないです) (Formal: 行きたくありません) (“I don't want to go”) · Casual: 行きたくない
• Past Affirmative: 行きたかったです(いきたかったです) (“I wanted to go”) · Casual: 行きたかった
• Past Negative: 行きたくなかったです(いきたくなかったです) (Formal: 行きたくありませんでした) (“I didn't want to go”) · Casual: 行きたくなかった
• Connective te-form: 行きたくて(いきたくて) (“I wanted to go, and so...”)

The First-Person Monopoly & Foreigner Traps

• Trap 1: The Privacy of Mind (Third-Person Desires): In Japanese, you cannot state someone else's internal state as absolute fact. Stating *田中さんは日本に行きたいです sounds telepathic and rude! To report someone else's desire, use observed behavior:
• Visible craving: 田中さんは日本に行きたがっています。(たなかさんは にほんに いきたがっています。) (“Tanaka seems to want / is showing signs of wanting to go.”)
• Hearsay: 行きたいそうです(いきたいそうです) (“I heard they want to go.”)
• Direct quote: 行きたいと言っていました(いきたいと いっていました) (“They said they want to go.”)

• Trap 2: The Awkward Invitation: Never invite a guest, customer, or teacher by asking 何を食べたいですか or 来たいですか! Interrogating a superior's raw internal desires feels blunt. Use considerate invitations instead: 〜ませんか (“Won't you join?”) or 〜いかがですか (“How about...?”).

• Trap 3: たい vs ほしい: たい attaches strictly to verbs (actions you desire to do: 食べたい). ほしい attaches strictly to nouns with が (tangible items you desire to receive or possess: 新しい本がほしい). Never say *寿司を食べほしい!