Is the letter Y a vowel or a consonant? The answer is obviously that it’s both, but this is an important question for those who want to understand our spelling system, and it’s also a nice exercise in classification.

It’s not often that you have a chance to teach spelling and thinking skills at the same time.

First, Y must be a consonant in words such as “yellow” and “young” because of its effect on a preceding indefinite article, “a” or “an”. We write (and say) “a yellow bird” or “a young man”, and since the general rule is that we use “a” only before a consonant, “yellow” and “young” must start with a consonant.

In any case, Y sounds like a consonant; or rather, it sounds just as much like a consonant as, say, the W in “wet”. Nobody hesitates to call W a consonant, so why not Y? It’s true that they both sound a lot more like a vowel than bog-standard consonants such as P and D do. But the point is that Y is about as vowel-like or consonant-like as W, and we all agree that W is a consonant, so Y must be too.

So far, so good. The problem, of course, is that you can argue just as persuasively that Y is a vowel in words such as “by”, “fly” and “lady”.

This makes it harder to classify Y than other letters.

Here’s the evidence:

* In “by” and “fly” it must be a vowel because every word contains a vowel, and B is an even worse candidate than Y. This general rule is very powerful, and a vital part of every writer’s toolkit.

* In “fly” and “lady” it must be a vowel because it turns into the vowel I in the plural (giving “flies” and “ladies”). Why should the plural ending turn a consonant into a vowel? In fact, it makes some sense to think of Y as a special way of writing I when it’s at the very end of a word, because native English words never do end in I. (Words like “cacti” and “spaghetti” are foreign imports, reflecting the spelling of Latin and Italian.)

* Once again, Y sounds like a vowel in each of these words because it supports an entire phonetic syllable, which could be a beat in a poem.

But what about “boy”? Why aren’t we even tempted to write “boies” as its plural?

We think it’s because Y is a consonant here too, just like (say) the G of “bog”; but you may prefer to say it’s part of a complex vowel, like the I of “boil”.

Here you can argue either way, so give it to the class to think about.