Words with an alternation of the vowel include man/men, foot/feet and mouse/mice. The words leaf/leaves and knife/knives change f to ves. In the words child/children and ox/oxen the plural ends with -en. Word pairs such as deer/deer and moose/moose are the same in the singular and plural.
A few plurals do not follow those patterns. The plural of cactus is cacti, the plural of phenomenon is phenomena and the plural of die is dice. Other examples include analysis/analyses and thesis/theses.
English plurals are quite regular. However, a few do not end with the suffix -s/-es. A number of irregular plurals have an alternation of the vowel.
