There is no logic to plurals. I think this poem is by the venerable Bead who was complaining about the implementation of English 1.0 beta.
We’ll begin with a box, and the plural is boxes;
But the plural of ox should be oxen not oxes.
One fowl is a goose, but two are called geese,
Yet the plural of moose should never be meese.
You may find a lone mouse or a nest full of mice,
But the plural of house is houses, not hice.
If the plural of man is always called men,
Why shouldn’t the plural of pan be called pen?
If I spoke of my foot and showed you my feet,
When I give you a boot, would a pair be called beet?
If one is a tooth and a whole set are teeth,
Why shouldn’t the plural of booth be called beeth?
If the singular is this, and the plural is these,
Why shouldn’t the plural of kiss be kese?
Then one may be that, and three would be those,
Yet the plural of hat would never be hose.
We speak of a brother and also of brethren,
But though we say mother, we never say methren.
So plurals in English, I think you’ll agree,
Are indeed very tricky, singularly.