Desiderative 〜たい: Formation Table | Japanese Grammar

〜たい is how Japanese says "I want to (do something)," and its formation is refreshingly simple: take the ます-stem and add たい. 書（か）く → 書きたい, 食（た）べる → 食べたい. The catch — and the whole reason this page exists — is what happens after you build it: たい is not a verb, it's an い-adjective, so its past isn't ×書きたいだった but 書きたかった. Master that one fact and the rest is bookkeeping.

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Everything downstream of たい follows the い-adjective rules you already know from 高（たか）い. If you can conjugate 高い → 高くない → 高かった, you can conjugate 書きたい → 書きたくない → 書きたかった. It's the same machine.

The formation table

たい attaches to the 連用形（れんようけい）/ ます-stem — the same stem that carries ます, た, and たい alike (that shared stem is the subject of the ます-stem uses page). 書く is the anchor.

Verb	Class	ます-stem	＋たい	reading
書く	五段	書き	書きたい	kakitai
飲む	五段	飲み	飲みたい	nomitai
会う	五段	会い	会いたい	aitai
食べる	一段	食べ	食べたい	tabetai
する	irregular	し	したい	shitai
来る	irregular	来（き）	来たい	kitai

Note the two irregular stems: する contributes し (→ したい), and 来る contributes き (→ 来たい, read きたい — not くたい, not こたい). Because they both use their ます-stem, if you know 来ます (きます) you already know 来たい (きたい).

今日はもう疲れたから、早く帰りたい。

kyō wa mō tsukareta kara, hayaku kaeritai

I'm already tired today, so I want to go home early.

次の連休、温泉に行きたいなあ。

tsugi no renkyū, onsen ni ikitai nā

I really want to go to a hot spring next long weekend.

たい inflects like an い-adjective

Once 書きたい exists, treat it as a plain い-adjective. The final い does all the work — negatives, past, te-form, everything.

Form	書く example	reading
plain nonpast	書きたい	kakitai
negative	書きたくない	kakitakunai
past	書きたかった	kakitakatta
past negative	書きたくなかった	kakitaku nakatta
te-form	書きたくて	kakitakute
conditional ば	書きたければ	kakitakereba
polite	書きたいです	kakitai desu

The single most valuable row is the past: 書きたかった, not ×書きたいだった. English "wanted to" is one word, so learners instinctively slap a past-tense marker on the end (たい＋だった). But たい's tense lives inside the adjective — たい → たかった — exactly as 高い → 高かった.

本当は行きたくなかったんだけど、断れなくて。

hontō wa ikitaku nakatta n da kedo, kotowarenakute

Honestly I didn't want to go, but I couldn't say no.

ずっと会いたかったよ。元気だった？

zutto aitakatta yo. genki datta?

I've wanted to see you for so long. How have you been?

週末はどこにも行きたくなくて、一日中ゴロゴロしてた。

shūmatsu wa doko ni mo ikitaku nakute, ichinichijū gorogoro shiteta

I didn't want to go anywhere all weekend, so I just lazed around all day.

The object can shift を → が

With a 〜たい clause, the object of a transitive verb may take が instead of を, especially when the desire itself is what's being spotlighted. 水（みず）を飲む ("drink water") becomes 水が飲みたい just as readily as 水を飲みたい. Both are correct in modern Japanese; が leans traditional and emphasises the wanting, を leans neutral and is standard in longer or more formal clauses. The full decision is on the を vs が with 〜たい page.

喉がカラカラだ。冷たい水が飲みたい。

nodo ga karakara da. tsumetai mizu ga nomitai

My throat is parched. I want to drink some cold water.

ねえ、今日の夜、何が食べたい？

nē, kyō no yoru, nani ga tabetai?

Hey, what do you want to eat tonight?

Other people's desire: hand it to 〜たがる

Here's a restriction with no English parallel: you can't flatly assert someone else's inner feeling. 弟（おとうと）はアイスを食べたい, said as a bare statement about your brother, sounds wrong to Japanese ears — you can't see inside his head. For third-person desire, Japanese switches to 〜たがる ("shows signs of wanting"), which turns the feeling into observable behaviour and conjugates as a 五段 verb: 食べたがる → 食べたがっている. The full treatment is on the 〜たがる page.

子供が朝からずっと公園に行きたがっている。

kodomo ga asa kara zutto kōen ni ikitagatte iru

My kid has been wanting to go to the park all morning.

妹は本当は来たがっていたのに、仕事で来られなかった。

imōto wa hontō wa kitagatte ita noni, shigoto de korarenakatta

My sister actually wanted to come, but she couldn't because of work.

Softening たい in formal speech

Bare 〜たい can sound bluntly self-centred in formal settings ("I want…"). The standard softener is 〜たいと思（おも）います ("I'd like to…"), which reframes the desire as a considered intention.

本日は、弊社の新サービスについてご説明したいと思います。

honjitsu wa, heisha no shin-sābisu ni tsuite go-setsumei shitai to omoimasu

Today I'd like to explain our company's new service. (formal presentation)

For English speakers: "want to" is a verb, "たい" is an adjective

This is the whole mental shift. In English, "want" is a verb — you conjugate it (want → wanted) and leave the second verb as a bare infinitive ("want to go"). Japanese does the reverse: the "want" fuses onto the main verb as a suffix, and the fused word behaves like an adjective. So "I wanted to go" isn't "want(past) + go"; it's 行きたかった — the destination verb wearing an adjective's past ending. Once you stop looking for a separate "want" verb and start treating 〜たい as い-adjective machinery, the errors vanish.

Common mistakes

1. ×書きたいだった — treating たい like a noun/verb for the past. たい is an い-adjective; its past is たかった.

❌ 昨日、映画が見たいだった。

Wrong — たい inflects as an い-adjective, so the past is 見たかった, never ×見たいだった.

✅ 昨日、あの映画が見たかった。

kinō, ano eiga ga mitakatta

I wanted to see that movie yesterday.

2. ×食べたいじゃない for the negative. The negative of an い-adjective is くない, so it's 食べたくない — not the な-adjective/noun pattern じゃない.

❌ 今は何も食べたいじゃない。

Wrong — たい negates like an い-adjective: 食べたくない, not ×食べたいじゃない.

✅ 今は何も食べたくない。

ima wa nani mo tabetakunai

I don't want to eat anything right now.

3. Stating a third person's desire flatly with たい. For someone else, use 〜たがる (or hedge with らしい・そう).

❌ 弟は新しいゲームを買いたい。

Wrong as a flat assertion — you can't directly state another person's inner desire. Use 〜たがっている.

✅ 弟は新しいゲームを買いたがっている。

otōto wa atarashii gēmu o kaitagatte iru

My brother wants to buy the new game.

4. Misreading 来たい as ×くたい / ×こたい. 来る's ます-stem is き, so 来たい is きたい.

❌ また日本にくたい。

Wrong reading — 来たい is built on the ます-stem き, so it reads きたい (kitai).

✅ また日本に来たいです。

mata nihon ni kitai desu

I want to come to Japan again.

Key takeaways

Build 〜たい on the ます-stem: 書き → 書きたい, 食べ → 食べたい, し → したい, 来（き）→ 来たい.
たい is an い-adjective: 書きたくない, 書きたかった, 書きたくて, 書きたければ — never ×書きたいだった.
The object may shift を → が (水が飲みたい), especially to spotlight the desire.
Third-person desire uses 〜たがる (行きたがっている), because you can't assert another person's inner feeling directly.
Soften formal 〜たい with 〜たいと思います.
来たい reads きたい (ます-stem き), not くたい or こたい.

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