Impossible objects are drawings of apparently three-dimensional objects which look correct when their individual parts are examined, but when you look at the object as a whole, it turns out to be not realizable. One of the most famous examples was created by D. H. Schuster and published in a psychology journal in 1964. The paper was titled "A New Ambiguous Figure: A Three-Stick Clevis", and said figure looks like this:
As emphasized by the colored background, the top of the object resembles the upper part of a stirrup (which has the basic form of what is known as a "clevis") and the bottom of the object looks like three parallel rods. Somewhere in between lies the ambiguity that destroys the three-dimensionality. Martin Gardner referred to such drawings as "undecidable figures".
The three-stick clevis has since gone by many other names: blivet, devil's tuning fork, widget, and poiuyt.
Mad Magazine used "poiuyt" as the name for the above blivet when they featured it on their March 1965 cover. The difficulty you may be having in deciding how to pronounce "poiuyt" is due to its unusual origin. The word "QWERTY" was formed by starting from the left side of the top row of a typewriter and taking the first six letters. Applying the same technique to the other end of the keyboard you get the looking glass version of "QWERTY"... "poiuyt".
Just as perspective drawing was invented to allow us to make two-dimensional depictions of three-dimensional things, spelling was invented to allow transcription of spoken language. And just as we can draw objects that are logically inconsistent, so can we write combinations of letters that correspond to no spoken word.
"Poiuyt" has no apparent, standard, or authoritative pronunciation. Dictionaries ignore it. If the reader will indulge me, I will nominate it as our first impossible word.
Another candidate for impossibility is "balge" (as in "balge yellow"), a term that is listed in Merriam-Webster's Third New International Dictionary as having no known pronunciation and no known origin (as if it spontaneously generated on a piece of paper on some lexicographer's desk). "Balge yellow" has been defined as "a brilliant yellow color" and "sunflower yellow", so at least that part of its wordhood is known.
A 1976 survey of color names by the National Bureau of Standards identified
Even though no one seems to know how to pronounce "balge", it doesn't feel undecidable in the way that "poiuyt" does, probably due to the latter's discombobulating four consecutive vowels.
My third nomination for impossible word is YHWH which is the English version of the Hebrew word: יהוה. Controversy surrounds this word. It is used throughout the original Hebrew texts of the Old Testament as the primary name for God. Some pronounce it as "Jehovah" or "Yahweh". Since ancient Hebrew lacked was written without vowels, the correct pronunciation of יהוה is not known. There is a strong taboo against speaking this name in Judaism, so it may be that whatever correct pronunciation might have existed has disappeared due to lack of use. Some believe that the pronunciation is a secret preserved by only a few people in each generation. What I like best about this word is that there is another name you can use when talking about it: "the Tetragammaton" (from the Greek for "having four letters"). The undecidability of YHWH's pronunciation is in an entirely different class than that of poiuyt, but maybe a property of impossible words is that they are all impossible in their own ways. This one seems to be more of an arms-crossed, exasperated "Tetragammaton, you're impossible!" way.
I feel obligated to mention one word that I thought would be impossible but has turned out not to be: Mxyzptlk. Mister Mxyzptlk is a mischievous prank-playing imp from the fifth dimension who occasionally visits Earth to wreak havoc until Superman deals with him. The gimmick was that the only way to send Mister Mxyzptlk back home was to trick him into saying his name backwards.
While Mxyzptlk has been pronounced in a variety of ways throughout the years, allegedly the DC Comics editor gave an authoritative pronunciation early on: "mix-yez-PIT-elick". But I suppose that one could claim that it is in Mxyzptlk's trickster nature that the pronunciation of his name refuses to be nailed down.
Then there are heteronyms which are words that are spelled the same way but pronounced differently:
"bass" can rhyme with "glass" or "space".They're better classified as ambiguous than outright impossible.
"wind" can be pronounced with a short I (like the thing that blows) or a long I (the verb that describes forming a ball of yarn).
As heteronyms change pronunciation based on the context they are used in, they are analogous to the Necker Cube:
Rather than representing a figure that has no sensible three-dimensional realization, the Necker cube confounds the viewer because it has more than one realization. Most people initially see it as a wire-frame cube, viewed from the top, with the lower-left square as the front face. After studying the figure for some time, it may seem to suddenly shift to a cube seen from above with the upper-right square as the front. I find that I can switch between the viewpoints by focussing on a face that appears to be at the back of the cube which seems to cause it to pull forward.
The impossible word is an exceedingly rare thing because we tend to make up pronunciations for words, even if we have to break the laws of phonics. (Doing so yields ultraphonic words (words outside the range of normal phonics), such as Big Bird's pronunciation of ABCDEFGHIJKLMNOPQRSTUVWXYZ as a single long word by sneaking vowel sounds into strings of consonants like JKLMN.)
Spelling a word is a reductive, lossy process. Accents, tones, sarcasm, are all generally omitted. English orthography, in particular, requires collapsing the full spoken word into a few characters, introducing considerable ambiguity, but from this ambiguity is born many good things, like puns and poiuyts.
- On balge: According to an 1875 Bulletin from the National Association of Wool Manufacturers, balge yellow was "generally employed on cassimere for vestings". Google Books also has the recipe for dying wool balge yellow.
A word about the very cool font used for the IMPOSSIBLE graphic above: “ISOSIBILIA Typography Designed by Rodrigo Fuenzalida for Neo2. - [Back to footnote reference]