1
general::
Phrase(s): know someone from someone
to tell the difference between one person and another. • I don’t know Fred from his twin brother. • I know Bill from Bob, but I can’t tell most identical twins apart., Phrase(s): know from something
to know about something. (Used on the eastern seaboard.) • Do you know from thermostats? • You don’t know from anything!, Phrase(s): know something from something
to tell the difference between one thing and another. (Often with a negative.) • You don’t know a smoked herring from a squid! • She didn’t know a raven from a crow, and who does?
McGrawhill's American Idioms And Phrasal Verbs