what is it called when a term is converted from one form into another form? such as converting situation to situational. the change of the affix makes all the difference. what is that process called?

Answer 1

This is a process in morphology called derivation. Derivational affixes are ones that either change the word class (such as from a noun to adjective, as in this case) or drastically change the meaning of the word. An example of this latter case is the prefix 'un-' which could change a word like 'do' to 'undo,' thus creating the opposite verb.

This process is separate from inflection, in which affixes are added simply to show things like verbal agreement. In a case like 'I play' vs 'He plays,' adding '-s' to the end of 'play' does not drastically change the meaning of the word.

If you'd like to learn more about this topic, I suggest looking up the phrase "derivational morphology" as that is what this phenomenon is called. Hope this helps!