Not a clue.

Dear Word Detective: I’ve heard the saying “can tell a hawk from a handsaw,” or sometimes “can’t tell…,” but I have no idea what the saying means. Can you help? — Allan Pratt.

Absolutely, no problemo. But first, two questions of my own. One, have you actually heard someone say that phrase aloud (as opposed to reading it somewhere)? Secondly, if the answer is “yes,” where in the world do you live? I’d give my eyeteeth to live among people who actually use phrases like that. I was searching on Google News just now to see if any publications had used the phrase lately, and while only a few had in the past couple of decades, back in the late 19th and early 20th centuries it seems that nearly everyone knew the phrase. By the way, assuming that at some point in the future someone is going to invent a working time machine, why can’t I buy one now?

Meanwhile, back at your question, “to know a hawk from a handsaw” means to be able to correctly perceive reality, to be able to tell things apart, to generally know what’s going on and, at a minimum, not to be nuts. It comes from Shakespeare’s 1604 play “Hamlet,” Act II, Scene 2. Hamlet, who has been acting more than a bit loopy, gets into a conversation with the courtiers Rosencrantz and Guildenstern, in the course of which he hints that his apparent madness may be a tactical pose he adopts at specific times, and not true dementia, saying “I am but mad North North west; when the wind is Southerly, I knowe a Hauke, from a hand saw.”

There is now apparently general agreement that the “hand saw” in that line was originally “heronshaw,” a dialectical English form of “heron,” meaning that Hamlet was contrasting two types of birds, rather than a bird and a carpentry tool. It’s also possible that he meant “heron” to symbolize the prey of a hawk, as he had, at this point in the conversation, figured out that Rosencrantz and Guildenstern, his childhood friends, had been corrupted to his detriment by his murderous uncle.

Despite its apparent genesis as a typographical error, “to know a hawk from a hand saw” gained wide currency almost immediately as an idiom meaning “wide-awake, aware and competent” (“He’s a pretty spruce Fellow, Madam, and … knows a Hawk from a Handsaw, as the saying is,” 1677). Interestingly, Shakespeare had used the same type of metaphor in his earlier comedy “The Merry Wives of Windsor” (“We’ll teach him to know Turtles from Jayes”), but that one didn’t catch the public imagination as “to know a hawk from a hand saw” did. Of course, the alliteration of “hawk” and “hand saw” (or “heronshaw”) didn’t hurt, and neither did the presence of “Hamlet” in the core curriculum of schools for many years.

The underlying sense of “to know a hawk from a hand saw,” that of the ability to accurately perceive things as a measure of sanity, awareness, or being “with it,” has taken many other forms in popular culture. Such venerable phrases as “to know the time of day” (1897) or “to know what’s what” (16th century) have been joined by more colorful and jocular measuring sticks such as “to know how many beans make five” (1830), the simpler form “to know beans” (1833), and “to know one’s onions” (1922). The 20th century saw the rise of stronger phrases, most often used in the negative, including “not to know your arse from your elbow” (1930), “not to know one’s rump from a hole in the ground” (1936) and stronger variants, and not to know excrement “from Shinola,” which was a popular brand of shoe polish in the US in the first half of the 20th century. My personal favorite on this theme dials back the vulgarity and goes for the absurd: “Not to know if it’s Piccadilly or Wednesday,” Piccadilly being a street in London (“A piece of ice caught me a devil of a welt on the head and for a moment I didn’t know if it was Piccadilly or Wednesday,” 1918). I know the feeling.