I usually find "&" in the trade name, say, "John & Company". I do not find "&" being used in sentences. What is the correct rule of usage of "&"? When can "and" be replaced with "&"?
It's more of a choice rather than a norm. 23andMe is an example of 'and' instead of '&' in a company name. '&', however, is more common and is more prevalent than 'and'. For a formal usage '&' is widely used:
- Business names: e.g. AT&T
- Addressing couples: e.g. Mr. & Mrs. Smith
- Academic papers (when there are multiple authors): e.g. Green, Black & White
Informally, it depends on the user.
This is largely a matter of style, rather than of the language itself. Most style guides traditionally frown upon the use of symbols to replace letters and words in formal communication; this goes not only for the ampersand (&), but for the percent sign (%), hash mark (#), and for that matter numerals, at least for smaller numbers. Suffice to say, emoji are right out.
Common guidance is that the ampersand should only be used in names, terms, or titles which are conventionally written with one (e.g. Marks & Spencer, P&G), but not as a generic replacement for and in body text. The Economist style guide is typical:
Ampersands should be used
1. when they are part of the name of a company (eg, AT&T, Pratt & Whitney);
2. for such things as constituencies where two names are linked to form one unit (eg, The rest of Brighouse & Spenborough joins with the Batley part of Batley & Morley to form Batley & Spen. Or The area thus became the Pakistani province of Kashmir and the Indian state of Jammu & Kashmir);
3. in R&D and S&L.
APA style says the last two names of authors in a citation may be joined with an ampersand, whereas MLA and CMOS say to write out and. The AP Stylebook even tweeted that ampersands should only be used in a company name or composition title - House & Garden - or in accepted abbreviations: B&B, R&B.
It stands for the Latin "et" ("and"); it is the two letters ("e" and "t") merged into one. It has been in use since 1st Century A.D.
It can be traditionally used in company names, or when one wishes to refer to the joint authorship of a book when quoting it more than once in an essay (i.e. "Duke & Diesel" rather than "Witty But Vulgar, by Archibald Duke and Humphrey Diesel"). One can also use it when taking notes: a poor man's shorthand, so to speak.
It is impolite to use it anywhere else.