Affixes can either be inflectional or derivational. This is determined by the level of effect the affix has on the word.
This affix does not change the meaning or word class of the word.
Rather, the root retains its word class (part of speech such as verb, noun, adjective, etc.) The meaning also remains the same. Inflectional affixes include
-s morpheme for plural nouns, e.g. BAGS (BAG+S) S doesn’t change the meaning. It doesn’t also change the word class. The word is noun still.
– s morpheme for singular verb, e.g. LOVES (LOVE+S)
-ED morpheme to show past tense of the verb
– S showing possession as in JOHN’S
– ER when it shows comparison in adjectives as in TALLER (TALL+ER) Still adjective. Note that this is different from the ER in teacher which is TEACH+ER (TEACH is a verb but TEACHER is a noun)
-EST as a superlative form of the adjective.
A DERIVATIONAL AFFIX
will derive a new word. It means that when this affix is added to a word, the meaning of the word changes and similarly, the word class changes too. Look at the following words, for example:
FUNCTION is a noun but FUNCTIONAL is an adjective. -AL morpheme is derivational. Also, STABLE is an adjective but STABILITY is a noun. ITY changes an adjective to a noun. In fact, the IN- before the word also changes its meaning. A new word is derived.
Attempt the other words. This is why it is called a derivational affix.
The following affixes are derivational in English
-ity, -isy, -al, ia, ex-, un-, tal, ness, ment, etc.