There has been innumerable entries on the idiosyncrasies of English when it comes to grammar, tense and plurality. This one simply is the best!
We’ll begin with a box, and the plural is boxes;
But the plural of ox became 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;
Yet 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 show you my feet,
And 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?
Then one may be that, and three would be those,
Yet hat in the plural would never be hose,
And the plural of cat is cats, not cose.
We speak of a brother and also of brethren,
But though we say mother we never say methren.
Then the masculine pronouns are he, his and him,
But imagine the feminine, she, shis and shim.