Here's why:
* Suffix Definition: A suffix is a word part added to the end of a word to change its meaning or grammatical function.
* Function of "-s" and "-es": These suffixes are used to form the plural of nouns (e.g., cat -> cats, box -> boxes) and the third-person singular present tense of verbs (e.g., walk -> walks, dance -> dances).
Therefore, because they are added to the end of words and change their grammatical function, "-s" and "-es" fit the definition of suffixes.