ほしい vs. たい

A question people often have about hoshi 欲しい, or rather, hoshii ほしい, an auxiliary adjective that means "want" in Japanese, is: what's the difference between hoshii and tai たい, another auxiliary which also means "want" in Japanese?

• Difference in Usage
• Moraitai もらいたい
• Conjugation

Difference in Usage

Well, the difference is simple: -tai ～たい defaults to saying "I want to do" while hoshii ほしい defaults to "I want you to do." For example:

• shinitai 死にたい
  [I] want to die.
• shinde hoshii 死んでほしい
  I want [you] to die.

Another example:

• koroshitai 殺したい
  [I] want to kill [someone].
• korosaretai 殺されたい
  [I] want to be killed [by someone].
• koroshite hoshii 殺してほしい
  [I] want [you] to kill [me].
  [I] want [you] to kill [someone].
  [I] want [someone] to kill [someone else].

• nigetai 逃げたい
  [I] want to run away.
  [I] want to escape.
• nigete hoshii 逃げてほしい
  [I] want [you] to run away.
  [I] want [you] to escape.

Some less edgy examples:

• oshietai 教えたい
  [I] want to teach.
• oshiete hoshii 教えてほしい
  [I] want [you] to teach [me].

• yomitai 読みたい
  [I] want to read.
• yonde hoshii 呼んでほしい
  [I] want [you] to read [something] [for me].

• akirametai 諦めたい
  [I] want to give up.
• akiramete hoshii 諦めてほしい
  [I] want [you] to give up.

Another big difference is that, because -tai ～たい is always attached to verbs, only hoshii 欲しい can be used to say you want a noun.

• keeki ga hoshii ケーキが欲しい
  Cake is wanted.
  I want cake.
• *keeki ga tai ケーキがたい
  (this is wrong.)

Moraitai もらいたい

Note that, in many cases, hoshii is practically synonymous with the verb morau もらう plus -tai, that is, moraitai もらいたい. See:

• tsukuru 作る
  To build. To make.
• tsukuritai 作りたい
  [I] want to build [something].
• tsukutte morau 作ってもらう
  To have [you] build [something] [for me].
  To have [someone] build [something].
• tsukutte moraitai 作ってもらいたい
  [I] want to have [you] build [something] [for me]
  [I] want to have [someone] build [something].
• tsukutte hoshii 作ってほしい
  [I] want [you] to build [something] [for me]
  [I] want [someone] to build [something].

Conjugation

Lastly, as you may have already noticed, hoshii is added to the te-form of verbs, while -tai ～たい suffixes the connective form, the ren'youkei 連用形.