Student or Learner
Hello, can somebody explain to me the difference between inflectional and derivational suffixes? If derivational suffixes create a new word belonging to a different part of speech, how come "firmly" is inflectional?
Thank you in advance.
 Add the suffix -s to the singular noun dog and it become a plural noun dogs. There is no change in category. They are both nouns.
 Add the suffix -ly to the adjective firm and it becomes the adverb firmly. There is a change in category: an adjective becomes an adverb. This is derivation.
In short, derivation changes a word's category; inflection, on the other hands, does not alter a word's grammatical category.