Why the plural form of play is plays not plaies?

The plural form of "play" is "plays" because of a historical change in the English language called the Great Vowel Shift.

Here's a breakdown:

* Old English: In Old English, the word for "play" was "plega." The plural form was "plegan." This ending "-an" was common for plurals in Old English.

* Middle English: During the Middle English period (roughly 1150-1500), the Great Vowel Shift occurred. This was a major change in how vowels were pronounced. The "a" in "plegan" shifted to a sound closer to "ay."

* Modern English: The spelling evolved from "plegan" to "playes" and finally to "plays." The "-es" ending became the standard plural marker for nouns, replacing the older "-an" ending.

So, "plays" is the correct plural form of "play" due to the historical evolution of the English language, including the Great Vowel Shift and the standardization of "-es" as the plural ending.