Caol le caol agus leathan le leathan
The golden rule for spelling in Irish, caol le caol agus leathan le leathan, means slender with slender and broad with broad. The terms slender and broad refer to two categories of vowels.
- The broad vowels are a, o, and u.
- The slender vowels are i and e.
The rule caol le caol agus leathan le leathan means that the vowels on either side of a consonant (or group of consonants) should agree; they should both be broad or both be slender. The rule is primarily used when you add an ending to a word (e.g., when conjugating a verb). To satisfy the rule you may need to add a vowel between the word and its ending. Understanding this rule will help you guess the correct spelling so you can look it up in a dictionary. There are a few words that do not satisfy this rule, but mostly they are common words that you probably already know, like anseo and ansin.
Even without knowing a single word of Irish, you can apply the rule to catch many spelling mistakes! Let's try a few examples:
Focus on the consonant in the center, l, and look at the vowels immediately before and after. The vowel before, o, is broad, and so is the vowel after, ú. This word follows the rule, so there aren't any obvious spelling mistakes here. (In fact, it is spelled correctly.)
Focus on the consonant group in the center, cf, and look at the vowels immediately before and after. The vowel before, a is broad, but the vowel after, i is slender. This looks like a mistake! (In fact, the correct spelling is glacfaidh).
The flanking vowels, o and a are both broad, so this word follows the rule.
The flanking vowels, i and e are both slender, so this word follows the rule.
Uh oh! The vowel before, i, is slender, but the vowel after, a is broad. (In fact, the correct spelling is dóimid).
Now you are ready to find spelling mistakes in that letter from your Gaeilgeoir friend.
Note: I originally published this article on E2.