There's only one word in Hebrew (or maybe two, but really one) in which the same letter appears four times in a row. Can you think of it? The answer is at the end of the column. Three identical letters in a row is more common, and two is positively mundane. The issue comes up because we just learned that a dagesh marks a double letter in Hebrew, as, for example, in "Shabbat," which gets but one bet. If a double letter gets written as a single letter with a dagesh, how is is possible to have double letters after all, to say nothing of triple and even quadruple? The answer is that, by and large, only double letters with no vowel between them are candidates for dagesh. So in the Hebrew word gag ("roof"), the vowel /a/ blocks the dagesh process. (The word gag brings up another puzzle: How many words can be written with only one letter? I've got 24, also at the end of the column.) Of course, nothing is so simple, because it's not always clear what counts as a vowel, so it's not clear what blocks the dagesh process. Once again, we use the notion of base word, which is to say, the singular masculine third person. When two letters have no vowel between them in a base word, they get written as one letter with a dagesh. That's why "Shabbat" gets a bet with a dagesh (it's a base word), and why dibber ("he spoke") also gets a dagesh in the bet, but sov'va ("she spun") gets double bets, with no dagesh. But the matter is a little more complicated, because some suffixes meld with their base words, and others don't. Yashan means "he slept." It's a base word. The derived form "we slept" ends with the suffix -nu ("we"), but it's yashanu, not yashan'nu, and it's spelled yud-shin-nun-vav, with - you guessed it - a dagesh in the nun, marking the fact that the root has a nun and so does the suffix. The suffix -ta ("you") works identically, which is why "you went on strike" is ata shavata (not ata shavat'ta). It's as though these suffixes are part of the base word. By contrast, the possessive suffixes, like -cha ("yours") do not behave like part of the base word, and they do not merge with the letter before them. So "your king" is malk'cha, with two kafs. Prefixes also stay separate, so "in a house" is b'vayit. And now to the puzzles. In which word does the same letter appear four times in a row? And which words can be written with only one letter? Turning to the second one first, we find a handful of two-letter words: gag ("roof"), dad (a rare word for "nipple"), vav ("hook," and also the letter vav), zaz ("he moved"), hah ("nose ring"), kach ("so"), mem (the letter mem), sas ("moth"), tzatz ("he popped up"), rar (a kind of fish), tat (the prefix "under-"), tet ("giving") and a no fewer than four words spelled shin-shin: shesh ("six"), shesh ("white linen"), shesh (a poetic form of shayish, "marble"), and sas ("he rejoiced"). So that's 15 biliteral words. To get the triliteral words, we need to add a bit a grammar, because while Arabic has a lovely word yayaya ("he wrote the letter ya [yud]"), Hebrew has nothing parallel. There are no simple words that triplicate letters. But we do have the prefixes she- ("that") and mi- ("from"), as well as the suffixes -o ("his") and -am ("theirs"). So we can build sheshesh ("that six" or "that marble" or "that white linen"); shesas ("that he rejoiced"), though we have to count shin and sin as the same letter; mimem ("from a mem"); memam ("their mem"), spelled the same way as mimem; and finally the truly bizarre vav-vav-vav, which spells vavo ("his hook"). The quadriliteral word, the most difficult part of the second puzzle, is also the answer to the first puzzle. Mem-mem-mem-mem spells mimemam ("from their mem"), and is the only Hebrew word to put four identical letters in a row. But if you thought of uvavo ("and his hook") you win half credit. It should be spelled vav-vav-vav-vav, but an arcane rule of Hebrew spelling generally prevents it. The writer teaches at HUC-JIR in New York City.