Turning nouns into adjectives

[michellegrady]

I get this question often:

What are the rules on turning nouns into adjectives? Is there any general rule?
I have one friend in specific who is very confused about this.

For example, how do I explain why you would say:

The salt water
The dirt road
business trip
bean soup
rose garden

etc.

instead of:

salty water
dirty road
and in the last two cases...
soup made of beans
garden of roses or garden with roses.

Is there a clear explanation?

Thanks so much!

[Jo]

Some explanations about noun as adjective are shown at:
http://www.englishclub.com/grammar/nouns-adjective.htm

The above page doesn't answer all your questions, but I would point out that there is a vast difference between a dirt road and a dirty road. One could potentially have a "clean dirt road".

[michellegrady]

Thanks a lot! Yes I've explained that often using the adjective instead of the noun (in the case of 'dirty road' and 'dirt road' can change the meaning drastically.

This information will be helpful, I'm sure.