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OISHISOU! TABETAI!

たべたい！
I want to eat some!
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TANOSHISOU! IKITAI!
Tabetai!
When we add たい to the verb stem, we change the meaning of the verb to 'want to (do)' something. 
Begin with the -ます form of the verb. Drop the -ます and replace with -たい  です.
ぎょうざ  を  たべます。
  • I will eat gyouza.
ぎょうざ  を  たべたい  です。
  • I want to eat gyouza.
ヘリコプター  に  のります。
  • I will ride in a helicopter.
ヘリコプター  に  のりたい  です。
  • I want to ride in a helicopter.
ゲーム  を  します。
  • I will play video games.
ゲーム  を  したい  です。
  • I want to play video games.
Note that the -たい form behaves like an -い adjective. So, in the negative it becomes -たくない, and in the past tense it becomes -たかった.
PRESENT TENSE: CHANGING AFFIRMATIVE TO NEGATIVE
やさい  を  たべたい  です。
  • I want to eat vegetables.
やさい  は  たべたくない  です。
  • I do not want to eat vegetables.​
USING -TAI AS A TRUE い ADJECTIVE
いきたい　ところ
  • place(s) you want to go
みたい　えいが
  • movie(s) you want to see
よみたい　ほん
  • book(s) you want to read
たべたい　もの
  • thing(s) you want to eat
EXAMPLE SENTENCES
いきたい　ところ　が　たくさん　あります。
  • There are lots of lots of places I/you want to go.  (This can also be used to imply that there are lots of places worth seeing.)
みたい　えいが　は　ぜんぜん　ありません。
  • There are absolutely no movies I/you want to see.  (This can also be used to imply that there are no movies worth seeing.)
よみたい　ほん　が　たくさん　あります。
  • There are lots of lots of books I/you want to read.  (This can also be used to imply that there are lots of good books worth reading.)
たべたい　もの　は　ぜんぜん　ありません。
  • There is absolutely nothing I/you want to eat.  (This can also be used to imply that the food is awful and there is nothing worth eating.)
PAST TENSE: CHANGING AFFIRMATIVE TO NEGATIVE
ジェットコースター  に  のりたかった  です。
  • I wanted to ride on the roller coaster.
ジェットコースター  に  のりたくなかった  です。
  • I didn't want to ride on the roller coaster.
Oishisou! Tabetai!  
わ～、おいしそう！にくまん  を  たべたい  です！
  • Wow, that looks yum！I want to eat steamed pork buns！
わ～、たのしそう！ジェットコースター  に  のりたい  です！
  • Wow, that looks like fun！I want to ride on the jet coaster!​
わ～、むずかしそう！たいそう  は  やりたくない  です。
  • ​Wow, that looks difficult. I don't want to do gymnastics！