Content or contents — when do I use which form?
I realize that the one is the plural form of the other, but they seem to be used interchangeably.
You should be aware where you're using it.
According to ldoce:
She kept the contents of the letter a secret.
water with a low salt content
The content of the media course includes scripting, editing, and camera work.
The graphics are brilliant. It’s just a shame the content is so poor.
The New Oxford American Dictionary entry for content has:
1. (usu. contents) the things that are held or included in something: he unscrewed the top of the flask and drank the contents | he picked up the correspondence and scanned the contents.
• [usually in singular] the amount of a particular constituent occurring in a substance: milk with a low-fat content.
2. the substance or material dealt with in a speech, literary work, etc., as distinct from its form or style: the outward form and precise content of the messages.
So, it tends to be used in the plural, except in certain particular cases.