Introduction to Morphology

Affixation is one way of making new words. Affixation is when we add a suffix (at the end of the word) or a prefix (at the beginning of the word) to a base or root word to change the meaning or the part of speech. 

This is also called derivation. 

This type of word formation can either preserve (class-preserving) or change the class of the word (class-changing), for example a verb becomes a noun.

Prefixes are usually class-preserving.

Suffixes are usually class-changing.

Example 1: 

happy --> happily

adjective --> adverb

Here the -ly suffix is class-changing because the adjective happy becomes an adverb. 

Example 2:

agree --> disagree 

verb --> verb 

Here the dis- prefix is class-preserving because only the meaning of the verb changes, not the part of speech.