|Definition - The ampersand (&) is a phonogram that stands for the conjunction and.|
Love & marriage goes together like a horse & carriage.
1. Don't use it in place of the word and in formal writing.
Four score & twenty years ago … (bad)
2. Don't put spaces around an ampersand when it is used within an initialism.
3. Do put spaces around an ampersand when it is used in a company name.
Smith & Co.
4. Use it to cite sources within the flow of the text.
The alternative view (Smith & Jones, 2007) states that ….
Etymology - The symbol was coined as a ligature of the Latin word et, and.
Note: According to the Online Etymology Dictionary, the word ampersand was coined as a contraction of and per se and, which means "(the character) '&' by itself is 'and'"
Oxford English Dictionary - Its first citation is from 1837: "He has hardly learned what Ampersand means, afore they give him a horse."
(Haliburton Clockm. (1862) 399)
Your etymological explanation comes close but misses the mark. My understanding is that this phrase was incorporated in the rote learning that youngsters once had to digest in memorizing the alphabet. In these pre-modern times, the alphabet began with "Aa"; followed by "&"; followed by "Bb"; "Cc"; etc. Thus the student would recite "A per se A"; "&(pronounced A) per se and"; et al., thereby distinguishing the two possible uses for the capital letter A.
I got my info from the OLED, which is — as far as I can tell — always bang on. (ODLTguy)
(Ian J. Wilson, Westerville, Ohio)