Mnemosyne was the ancient Greek goddess of memory, the mother of the Muses. From a word related to her name we get the word "mnemonic" (a device for remembering something), one of the few English words starting with a silent 'm.'Mnemonics can be used to aid fallible human memory in recalling numbers, pronunciations, the order (and often initial letters) of a sequence, even the correct action to take in particular circumstances. For instance:
- The order of the phases of the moon (and thus, whether the current appearance of the moon indicates waxing or waning) can be remembered with the phrase "What's up, DOC?": D indicates a (waxing) half-moon with the curve on the right, O indicates a full moon, and C indicates a (waning) crescent moon with the curve on the left, heading toward a new moon. (Dominus points out, by the way, that the word "crescent" is related to "crescendo" and originally referred only to the waxing moon growing larger, not to the shape we now call a crescent; the waning moon could thus more accurately be called a "decrescent" moon—though I prefer the obsolete term "diminuent." Unfortunately, "crescent" starts with C and "decrescent" and "diminuent" start with D, which could lead to a backwards mnemonic if you think about it too much. So don't.) (Thanks to Laura Lemay for providing the term "decrescent.")
There are many mnemonics for remembering the first several digits of pi, usually by counting the number of letters in each word of the mnemonic. My favorites:
See I have a rhyme assisting,
My feeble brain, its tasks resisting.
May I have a large container of coffee?
(For more pi mnemonics, including quite a few non-English ones, see the pi mnemonics page.)
I have yet to hear a mnemonic for the digits of e, perhaps because it's less common to need to know those digits.
Most people, as I understand it, mispronounce Aleister Crowley's last name. He once wrote a verse to demonstrate how to pronounce it, which went something like this:
My friends call me Crowley
because they think I'm holy.
My enemies call me Crowley
because they wish to treat me foully.
- The initials for the names of the Great Lakes, in no particular order, spell out HOMES: Huron, Ontario, Michigan, Erie, Superior.
There are lots of mnemonics specific to particular professions or fields of study. I can never remember the ones for lobes of the brain, or geological ages; there's a Web page that lists some of them for those interested. Here are some field-specific mnemonics that have stuck in my brain over the years:
- Astronomers traditionally remember the order of the types of stars via the initial letters of the phrase "Oh, Be A Fine Girl, Kiss Me."
- Most musicians have heard "Every Good Boy Does Fine" [or Deserves Favor] as a mnemonic for the notes represented by the lines in the treble clef of a bar of music, reading upward from the bottom: EGBDF. The spaces between the lines spell out a word: FACE. The bass clef, oddly, has a mnemonic sentence for the spaces rather than the lines: "All Cows Eat Grass."
- Artists and rainbow-fanciers remember the order of the colors of the spectrum as a name: Roy G. Biv, for Red, Orange, Yellow, Green, Blue, Indigo, Violet.
- Anyone who's ever taken biology has probably been taught to say "King Phillip Came Over For Great Sex" to remember the taxonomic terms Kingdom, Phylum, Class, Order, Family, Genus, Species. (As with most ordering mnemonics, the assumption is that given initial letters you can remember the actual terms.)
- Mathematics students remember the order in which to perform mathematical operations with the phrase "Please Excuse My Dear Aunt Sally": parentheses, exponents, multiplication, division, addition, subtraction.
- And most Americans (among others) remember whether to set their clocks ahead or back for Daylight Saving Time with the phrase "spring forward, fall back." I have yet to hear a mnemonic, though, for remembering which of those times of year is the beginning of Daylight Saving and which is the end (and in fact I've heard people vociferously argue about which is which).
Many mnemonics take the form of two phrases with similar rhythms. Sometimes it can be hard to remember the mnemonic correctly—and if you get a mnemonic backwards, it's worse than no use. For instance:
Feed a cold, starve a fever.
It always takes me a little while to convince myself it's not "feed a fever, starve a cold." Though I gather neither of those is terribly good medical advice anyway.
And then there's the traditional rhyme to remember signs of good and bad weather:
Red sky in morning, sailors take warning.
Red sky at night, sailors delight.
Unfortunately, I always remember this second line as ending "...sailors take fright." Fortunately, I'm not a sailor, so my inability to remember the rhyme properly has yet to have serious effect.