What is the purpose of the words "simple,' plain, and "common"?

to appeal to as large of an audience as possible

they all mean the same thing, they explain or describe a noun.  

Explanation:

simple- means plain.

plain means simple.

definition of both:

plain= not decorated or elaborate; simple or ordinary in character.

simple= easily understood or done; presenting no difficulty.

they both meaning things that just aren't difficult to understand.

and common means=occurring, found, or done often; prevalent

basically occurringly found.

all words all have the same meaning generally, but techicnally they dont.

hope this helps :)

i think that the answer is substandard.

what book are we talking about here