Are there rules of usage when using the ampersand "&" instead of "and"?
Are they completely interchangeable?
The ampersand seems more casual, but I'm not sure.
There are very, very few acceptable uses of & in proper written English. Here are some of them:
& is especially common when joining names to indicate a firm or a partnership, for example, a law firm:
In abbreviations, when abbreviating "and", & is often used:
One rare usage is on envelopes addressed to a couple:
&c. is a rare and somewhat archaic looking abbreviation for etc.
Other than that it is vanishingly rare to see & in formal written English, although of course in informal email, text messages, notes, and handwriting, anything goes.
I looked through a couple of reference books and both of them said that the ampersand should only be used in company names.
Meaning-wise I think they are.
It's an abbreviation so one might use it more in less formal writing.
I cannot say this is correct but in use I find it very useful....
I often use "&" when two things are related directly but only in a series... example: Michel has experience in Marketing, Research & Design, and Business Management....
like I said, this most likely isn't correct but it makes sense, seems useful, and if enough people agree then we can change the rules & regulations.