Is there a difference between んがため and ために?

Question

My JLPT textbook has a section about the use of んがため, which they define as "making an effort in order to realize the intended purpose."

Which to me sounds like plain ol' ために.

For example, they have this example sentence:

祖父{そふ}は１００歳{さい}まで生{い}きんがために、食生活{しょくせいかつ}にはとても気{き}をつける。

Isn't that the same as saying:

祖父{そふ}は１００歳{さい}まで生{い}きるために、食生活{しょくせいかつ}にはとても気{き}をつける。

...?

Answer 1

Matt pretty much gave the answer, but I'm going to be cheeky and write a real answer, since I think the question deserves it.

This ん is not the negative, but a contraction of the archaic auxiliary verb む, which expresses intention, prediction etc. As the Goo article says, since the Heian period, it also appeared as ん, and since the Kamakura period as (よ)う. The latter is basically the modern Japanese volitional verb suffix.

I cannot think of any situation where the む form survives in modern Japanese. The ん form survives in certain fossilized constructs:

生きんがため in order to live
言わんとする intend to say

Incidentally, these could also be expressed with the (よ)う form:

生きようがため in order to live
言おうとする intend to say

Edit:

In terms of meaning, there is not much of a difference, but the んがため・んとする versions sound a bit more old-fashioned/solemn. So the difference in use is mostly stylistic.

Answer 2

This one had me up thinking and at first I thought it was something else, but more research lead me to the correct answer. :) Thank you, actually!

So, here is what the difference is:

1) 祖父は１００歳まで 生きるために 、食生活にはとても気をつける。

(My Grandfather took very good care of his diet in order to live until 100yrs of age.)

Here, ために is used in the more common way, (a)v.inf + ために + (b)v.inf/masu = b for the purpose of a

2) 祖父は１００歳まで 生きんがために 、食生活にはとても気をつける。

(My Grandfather took very good care of his diet in order to live until 100yrs of age.)

Here, it is saying the exact same thing... the difference is what precedes ため.

The 〜んがために is a contraction of 3 parts:

• The verb in imperfective form
• The が particle, which in Japanese is very similar to の
• and ため

Here is someone else's much better explanation of 未然形 / imperfective form: link