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.
Learn English – When to use & instead of “and”
ampersandconjunctionsword-choicewriting-style
Best Answer
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.