not know beans (about something)

To know nothing or next to nothing (about something). Don't ask me! I don't know beans about car engines. I'm fairly handy when it comes to fixing cars, but put me in front of a computer and I won't know beans.

Inf. to know nothing about someone or something. Bill doesn't know beans about flying an airplane. When it comes to flying, I don't know beans.

Also, not know the first thing; not know from nothing. Be ignorant about something, as in a poem published in the Yale Literary Magazine in 1855: "When our recent Tutor is heard to speak, This truth one certainly gleans, Whatever he knows of Euclid and Greek, In Latin he don't know beans." The beans in this colloquial phrase, dating from the early 1800s, signify something small and worthless; not knowing the first thing about something clearly shows one doesn't know anything about it at all; and the third slangy phrase, with its double negative, implies stupidity as well as ignorance, as in Poor girl, just starting out and she doesn't know from nothing.

Be quite ignorant about something. This colloquialism dates from the early nineteenth century, when beans denoted something small or worthless. However, from the mid-1800s to the early 1900s the converse, to know beans, meant to be quite knowledgeable. The latter has not survived, but we still hear, for example, “Don’t ask Harry’s advice; he doesn’t know beans about cars.” A more specific and much ruder variant is not know one’s ass from one’s elbow, which dates from about 1900 and denotes general stupidity. Other versions replace “elbow” with “hole in the ground,” but “elbow” is heard more often and has become a cliché. A 1963 citation has it, “These medics don’t know their asses from their elbows.”