know from something

know (someone or something) from (someone or something else)

To be able to distinguish a particular person or thing from someone or something else. Usually used in negative constructions. I've heard his name before, but I wouldn't know him from a stranger on the street. My father is so hopeless when it comes to technology that I'm surprised he knows a mouse from a monitor.
See also: know, something

not know from (something)

To not know anything about something. From Yiddish, heard primarily on the East Coast of the US. Why don't you just stay out of this, OK? You don't know from running your own business. Ah, don't mind her, Phil. She doesn't know from nothing.
See also: know, not

know from something

in. to know about something. (see also not know from nothing.) Do you know from timers, I mean how timers work?
See also: know, something