From the archives...
The following question was originally posted on the (now discontinued) LOE Forum.
As we're learning in Foundations D about adding suffixes, we were wondering about the combinations "day"+"ly" (daily) and "gay"+"ly" (gaily). These words seem to defy the rules as they both end in the two-letter vowel "ay" yet the "y" appears to change to "i". Following the rules, it seems they should be spelled "dayly" and "gayly."
You are correct! 'Gaily' and 'daily' do not follow the suffixing rules in the normal way. Their spelling is phonetic, but, strictly speaking, they are part of the approximately 2% of words that contain some sound or spelling that breaks one of the rules. Since they don't end in single-vowel Y, according to the rules you should just add the suffix, but instead they follow the rules for words that do end in single-vowel Y: the Y changes to I (or you could say that AY, two-letter /ā/ that may be used at the end, changes to AI, two-letter /ā/ that may NOT be used at the end).
These are the only words I know of where this happens (though you could say that the irregular past tense verbs 'laid and 'paid' are somewhat similar; they would be 'payed' and 'layed' if they were regular). Foundations D does not discuss these words, but they are covered in Essentials (Lesson 23, level B vocabulary section).
While the suffixing rules are quite accurate generally, they do seem to have a slightly higher percentage of exceptions than the rest of the rules.