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

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
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

know someone from someone

to tell the difference between one person and another. I don't knowFred from his twin brother. I know Bill from Bob, but I can't tell most identical twins apart.
See also: know

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?
See also: know

know from something

to know about something. (Used on the eastern seaboard.) Do you know from thermostats? You don't know from anything!
See also: know
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.

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
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.
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