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I have learned that when using a "-たい" form, when the sentence would normally require "を", you can use either "を" or "が", but "が" was actually preferred, "を" sounding unnatural.

I searched about the reason, but could only find the same, "が" is preferred, "を" doesn't sound natural to native speakers.

What is the reason? since the particle is before the "-たい" verb, it can't be a phonological deformation, so what is the logic behind it?

Thanks a lot!

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The rule that you are mentioning might be how it is initially taught, but there are plenty of exceptions to that rule. In none of the sentences 空を飛びたい, 家を出たい, この本を読み終えたい, can が be used instead of を. The question is still valid, though, and I don't know the answer. – dainichi Jan 24 '12 at 13:53
@dainichi Ah... damn right... How confusing – user1016 Jan 25 '12 at 6:59
up vote 4 down vote accepted

Originally I didn't think I had a full answer to this question, but in the end maybe I do.

たい is actually an adjective. When describing things with adjectives, が is used:


Youko's hair is long.

I think that adding たい to the ます form of a verb means it is no longer a verb, but rather an adjective. So don't think of たい form as a verb but rather an adjective, and this use of が should make sense.

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Great, I was thinking that -たい might be an adjective (given how -たい conjugation works), but didn't make the link with the が/を problem :) Thanks a lot! – Cristol.GdM Jan 15 '12 at 4:07
Hmm, ようこさんの髪が長いです is just unnatural. No native speaker would use the particle が for that sentence. – user1016 Jan 15 '12 at 5:59
@atlantiza san, As a native Japanese-speaker, I'd say we use ようこさんの髪'は'長いです and ようこさん'は'髪が長いです, but never ようこさんの髪が長いです。 – user1016 Jan 16 '12 at 14:22
@atlantiza san, Never mind. The particles are pretty tough, no? (Just as the English articles and prepositions are to me.) – user1016 Jan 16 '12 at 15:53
@atlantiza As simple and appealing as this explanation might be, I do not think it is correct. If you see my comment to the question, there are several cases where を has to be used. – dainichi Jan 24 '12 at 13:55

I'm not really sure if it makes sense to talk about 'logic', but I'll still try to see if I can add some system to the madness.

Japanese often uses が, not を, after what would typically be the object in English, when there's no actual action inflicted upon said object. 彼が好き, お金が欲しい, 日本語が分かる, りんごが食べたい, 字が読める, あいつが憎い.

One way to look at it could be: if for example you want to eat an apple (but haven't done it yet), is it really you doing something to the apple, or is it the apple doing something to you? You might argue that it is the latter. This might be why what English speakers regard as the object can take on the more subject-like が.

In the Indo-european languages that I know of, the topic of a sentence seems to be the subject by default (I want money, I can read letters), but Japanese, having a separate topic marker は, doesn't really have this restriction. After having said 私は, there is more freedom to make different parts of the sentence into the subject (even if the topic is often implied in Japanese).

However, there are also ~たい cases where only を feels much more natural (maybe が is even wrong):

 空を飛びたい <- (I) want to fly in the sky

 家を出たい <- (I) want to exit the house

In these cases, (maybe depending on who you ask) 空 and 家 aren't real objects, but rather the place that a motion takes place through (the former) and the place that a motion takes place from (the latter). I wouldn't be able to back up any claim as to why を is more natural here, but maybe this way of using を entered into the language at a different point in time, and therefore different rules apply (Linguists, please come to my rescue).

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Cool, I think that this is very interesting =) Btw to furthur analyze the situation, I was wondering is it possible to form the structure NをV~たい whereby N is not a "location"? – Pacerier May 28 '12 at 13:02

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