Hi Olivia,
I love how inquisitive your students are! This is a great observation on their behalf: we often double the final consonant in a word when adding a suffix (word ending) that begins with a vowel (such as < ed > or < ing >). But they are absolutely right that this doesn’t usually seem to apply to the < es > suffix. Many students will pick up on these sorts of patterns implicitly. Meaning, they know not to double the <x> in foxes simply because it “doesn’t look right”, and do not need the level of nuance described below laid out to them. So, while this level of detail may not be appropriate for all students, let’s explore this pattern more closely so you can best judge how to balance their inquisitiveness with their instructional needs.
We use < es > as a plural marker or a verb tense when our phonological sound system doesn’t allow for the /s/ or /z/ phoneme represented by < s >. Try to say the word push with only a /z/ sound afterwards; it doesn’t work! We need to pronounce this suffix with a vowel sound as well, which we say as /ĭz/ and spell as < es >. So, this suffix is a bit different than other vowel suffixes in that it is only used with a specific subset of words- namely, those that end with s, sh, ch, x, or z.
So let’s jump back to the consonant doubling rule. This rule needs a couple of conditions in order to apply:
1. The base word needs to end with one vowel and one consonant. This excludes most words that would need an < es > suffix. Both < sh > and < ch > use two letters, and most monosyllabic words that end with /s/ or /z/ are already spelled with a double consonant grapheme (< ss > as in boss or < zz > as in buzz), again negating the need to double any letters to add the suffix.
2. A part of condition #1 that is often unspoken, however, is that the one consonant can be seen (via letters) or heard (via sounds). This excludes words ending with < x >, as this letter represents two consonant sounds (/ks/ in the final position of words).
3. The penultimate (or second-to-last) sound needs to be a vowel spelled with one letter.
4. The vowel needs to be stressed. This characteristic is assumed for most monosyllabic words, but consider words like ‘bonus,’ ‘chorus,’ or ‘focus.’ Each of these words stresses the first syllable (and thus vowel) of the word, not the < u > before the final < s >, which is why the doubling principle does not apply.
By now, we’ve excluded most words that would use an <es> suffix from the doubling rule. But, that doesn’t mean the doubling rule doesn’t apply to <es>. I present two examples: whiz → whizzes and quiz → quizzes.
These conditions still leave a couple of words in the crosshairs, however: your ‘bus’ example and my addition of ‘gas.’ Both of these are interesting use cases: while not doubling the final consonant in the base words (i.e., ‘buses’ and ‘gases’) is most common, doubling this letter (i.e., ‘busses’ and ‘gasses’) is actually an acceptable spelling variation in both cases. It is probably not a coincidence that both of these words are shortened derivations from longer words (‘omnibus’ and ‘gasoline,’ respectively), so historical spelling conventions might have been disregarded accordingly (see also: the new slang of adding -maxxing to the end of words).
Thank you for sparking this curiosity in your students and instilling in them that there is actually a rhyme and reason for how words in English are spelled! But do make sure to strike a balance of what could turn into a long-winded discussion to justify the spelling of a very small number of words with instructional routines that will yield better returns!
