English is a difficult language to learn as they are many rules to follow. However, they are also many exceptions to the rules, such as the following sentences.

The plural of box is boxes.
But the plural of ox is oxen, not oxes.

One fowl is a goose, two are called geese.
The plural of moose should never be meese.

You may find a lone mouse or a nest of mice;
Yet the plural of house is house, 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 tooth and a whole set of 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 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.