grammar - Aren't がる and たがる the same thing?

In my JLPT practise book, it has two different entries, one to explain がる and one to explaining たがる. It offeres these example sentences to differentiate them:

うちの子{こ}は新{あたら}しいものを見{み}ると、すぐほしがる。

うちの子{こ}は甘{あま}いものを見{み}ると、すぐ食{た}べたがる。

I think they both mean to behave in a way that expresses the feeling described. So, ほしがる means to not only hope for, but to act like you hope for it, and as a result, everyone who sees you will know you are hoping. Something like that...　I don't have a pithy way of explaining がる.

So, if my definition is right, it seems both sentences are explaining essentially the same thing, and the only difference is one is attached to a verb, and the other is attached to a... um... something else. Whatever the grammatical category of ほしい is.

I'm confused about why the book is going out of its way to explain them separately.

Is there a difference in definition between がる and たがる beyond just how they fit into a sentence grammatically?

Answer

Expanding on @TsuyoshiIto's comment above, がる basically turns an イ-adjective (or "words which conjugate like" them, as he states) into a verb. Essentially means "acting this way" or "behaving in such a way":

• 寒【さむ】がる　→　To be cold (さむがり: a person who is always cold -- like me); "acting that you are cold"


• 怖【こわ】がる　→　To be afraid of something; "behaving such that you are afraid"

As a logical following of this, たがる is really just the 〜たい form of a verb (which conjugates like an イ-adjective) plus がる

• 食べたがる　→　("Acting like") Wanting to eat


• 行きたがる　→　("Acting like") Wanting to go


• 見たがる　→　("Behaving like") Wanting to see/watch

Since 〜たい cannot be used to directly state a 3rd party's desires (unless followed by something like 〜と思っている or 〜と言う), you must use 〜たがる.

×　となりのひとは新しいテレビを買いたい。
○　となりのひとは新しいテレビを買いたいと言った。
○　となりのひとは新しいテレビを買いたがっている。
○　となりのひとは新しいテレビを買いたいようだ。

I think the confusion in your examples is that you just happen to be using 食べたい (want to eat) and ほしい (generic "wants").

So there's really no need to think that there are two separate grammar patterns here. The pattern is really just がる. It just depends on whether you're attaching it to a regular イ-adjective or to a 〜たい イ-adjective.