How do nouns ending in Y preceded by a vowel form?

Nouns ending in "y" preceded by a vowel form their plurals by simply adding an "s".

Here are some examples:

* boy -> boys

* toy -> toys

* monkey -> monkeys

* valley -> valleys

This is because the "y" in these words is not acting as a consonant. The vowel before the "y" takes the sound of a consonant.