How do you tell if a word is singular or plural.?

Normally to indicate whether a Word is plural is by looking for an 's' at the end of the Word.
For example,

- cats
- trees
- birds
- carrots
- boys
- girls

However, there are some exceptions, where Words change when they are plural, and in this case, you must memorize them.
For example,

- 1 mouse, 5 mice
- 1 die, 3 dice
- 1 goose, 10 geese
- 1 ox, 7 oxen
- 1 knife, 6 knives
- 1 child, 3 children


Then you have some Words that do not change at all when they are plural.
For example,
- 1 moose, 10 moose
- 1 fish, 2 fish (there is an exception to this Word, as 'fishes' is correct to but means something different.)
- 1 deer, 5 deer