Safe or safety?

Sara asks:

Here I have a question lingering in my mind for a long time, the question is "What is the difference between adjective and noun when they two can both modify a noun?" The other day, I came across the Chinese sentence　....你不能让他和安全剃须刀睡在一起．Here, 安全剃须刀, the rendering to has two versions, one is "safe razor" and the other is "safety razor". I am a little confused about their differences and I hope you can throw some light on this.

My comments:

The example you gave, Sara, sounds a tad bizarre but your question is legit. I have a question for you regarding the bizarre part, but I shall answer your question first.

Noun as adjective, isn't it?

From personal experience, I do have a tip to give you, and that is to take it easy. When a noun is employed to modify another noun, it's probably because of a lack of an appropriate adjective for the purpose. It's as simple as that.

A safety measure (to ensure safety of the workers) taken at, say, a coal mine is different from a safe measure (one that is safe to apply). Here a safe measure doesn't sound right.

The rule of thumb, therefore, is to go with what sounds right to the ear.

Now, that sounds like something hard to achieve, doesn't it? But it shouldn't. Just give it a little time and be patient.

Hear other people (native speakers preferably) say it first and then copy it. This is especially important for learners of English as a second language, who tend to rationalize by trying to reconcile English grammar with that of their native tongue. Don't bother. Just speak the way the natives speak - when in Rome, do as the Romans do.

In the beginning, things may look hazy and confusing, but before long, they will clear up and you shall be more at ease.

It'll take some time, for sure. But then, what's the hurry? The goal is to get it right, not to get it first and fast (but wrong). As your feel for the English language improves, you'll be comfortable. All in good time.

If you want to experiment, go with what sounds right in English, rather than what would appear logical in Chinese. Home cooking, for example, is simple and natural in English. Domestic cooking, on the other hand, sounds, well, exactly like a piece of translation done by a novice Chinese translator.

Back to the example you gave, which sounds quite bizarre, as I said earlier.

If I understood you correctly, the Chinese sentence you meant to translate into English should read something like this: You should not let him go to bed with a (safe or safety) razor. And you want to take a stand between "safe" and "safety".

What I want to tell you is this: Save the trouble - just say "razor". In this case, you don't need to take sides because the razor doesn't need no modifier, noun or adjective, if you pardon the grammar. If it's a safe razor, which is likely the case here, that will be expected and therefore it will be unnecessary to say so. Who, you see, would want to do with an unsafe razor anyway?

If it were a safety razor, on the other hand, that implies that the knife would be one that would not get yourself hurt whichever way you choose to use it. Then it could very well just be some hullabaloo from the manufacturer. In that case, no-one should take that kind of propaganda seriously. So, in any case, you would sound more effective with a bare "razor" - leaving it there to stand on its own, stark and naked, that is, without being clothed and sheltered with any modifier, noun or adjective.

But that is not the "bizarre" part of your question. The bizarre part is, I ask you, Sara, why would anyone go to bed with a razor in the first place, be it a safe one or one of safety?