Digit four

Almost always the number four. The “for” reading needs a word slot to live in.

Placement is the whole tell. “Bring 4 chairs” is a count; “this one's 4 u” is compressed English, where the digit supplies the sound of “for” rather than a quantity. Same with 4ever, 4got, 4ward — the 4 lends its name, not its value.

If someone sends only “4,” resist the urge to decode. Ask which page, option or count they mean; the answer is usually boring.

Writing 4 for “for” dates you a little

It reads as SMS-era costume. When text messages were charged by the character, 4u and 4ever saved real space; now they mostly signal that you learned to text on a phone number pad, or that you're knowingly imitating someone who did. Among friends that's charming. In a message you want taken seriously, it's a smudge.

A separate track entirely: in Chinese cultural contexts four is widely treated as unlucky, because its pronunciation sits close to the word for “death.” That association belongs to the setting — a floor number, a gift quantity, a phone number — not to a stray 4 in an English sentence.