Use of ため with a negative verb in this sentence

Question

In my textbook Multimedia Exercises for Basic Japanese Grammar I came across this example sentence and I was completely puzzled:

これは、かぜをひかないためのサプリメントです。

All I have studied and read so far emphasized ため cannot be used with negative sentences, actually I had read an example that used 風邪をひかないように。。。

Why is ため used in this example? I googled to see if there were similar uses with negative verbs and got one Japanese page with this: 忙しい人たちの風邪をひかないためのTIPSをリサーチ.

Is it being used because of the の particle after ため? I'm very confused.

Answer 1

As you suggest, the following sentence does sound awkward.

かぜをひかないために、このサプリメントを飲んでいます。

The reason is that かぜをひかない is not something you actively do, and therefore, not suitable as a purpose.

The sentence below with ように, which denotes a desired state rather than a purpose, sounds much more natural.

かぜをひかないように、このサプリメントを飲んでいます。

If you still need to use ため, you should insert する as below so that the adverbial clause describes what you actively do to achieve a desired state, rather than the desired state itself.

かぜをひかないようにするために、このサプリメントを飲んでいます。

However, this distinction becomes less strict in a noun-modifying clause making かぜをひかないためのサプリメント much more acceptable, although some might find it a bit informal and still prefer かぜをひかないようにするためのサプリメント.

Answer 2

ため here is nothing special — just used in its most common meaning, "for the purpose of;" "the sake of."

Your sentence can be translated as follows:

これは、かぜをひかないためのサプリメントです。
This is the supplement for the sake of not catching a cold.

Since ため is a noun, it's followed with の. Again, nothing special. (The supplement for this sake; this sake's supplement)

風邪をひかないように, on the other hand, is an adverbial phrase. It roughly means "In a way of not catching a cold," and does not quite fit the context here.

If you're asking about ため with negative verbs, then it's simple — just use negative verbs as you would use positive verbs.

風邪を引くため
風邪を引かないため

Grammatically though, negative verbs of this sort (ending in ない) are actually い-adjectives, and because ため is a noun, then 引かないため and いい人 and 強い風 are all structurally equivalent (い-adj + noun).