Desiderative forms describe a wish. In other words, phrases such as "I want something" or "I want to do something". In Japanese, separate constructions exist for "I want you to …", and "He wants."

欲しい (hoshii)

The verb 欲しい (hoshii) is used when you want an object or result.

Inu ga hoshii desu.
I want a dog.

If you want a result, you will need the ren'youkei + てほしい (te hoshii). The ren'youkei + てほしい (te hoshii) is translated as "I want you to …". Please refer to our page on the ren'youkei conjugation for more information.

Kaette hoshii.
I want you to come home.

Ren'youkei + たい (tai)

The ren'youkei + たい (tai) means "to want", and expresses the desire to do something of the "first and second person": I, you, or we. The auxiliary verb たい (tai) is a verbal adjective like ない (nai) and is conjugated accordingly.

I wanted to see it.

Yomitai desu ka.
Do you want to read it?

Interestingly both が (ga) and を (wo) can be used for the object of desire.

Sashimi wo tabetai.
I want to eat sashimi.

Sashimi ga tabetai.
I want to eat sashimi.

Ren'youkei + たがる (tagaru)

The ren'youkei + たがる (tagaru) means "to want", and expresses the desire of the "third person": He, she, it, or they. The auxiliary verb たがる (tagaru) is a yodan katsuyou (or Group 4) verb and is conjugated accordingly.

Suzuki-san ga Pari wo mitagatta.
Mr Suzuki wanted to see Paris.

Shourai ni hon wo kakitagarimasu.
She wants to write a book someday.