Tom Murphy made all of this.
"Can I speak plainer?" Austen, Pride and Prejudice
" Currents do not show it plainer." Stein, Tender Buttons
"... the morning daylight appears plainer when you put out your candle." Franklin, Poor Richard's Almanack
“Everything is plainer when spoken than when unspoken.” Plato, Phaedrus
"Be plainer with me." Shakespeare, The Winter's Tale
"... things are seen plainer after the events have occurred ..." Grant, Memoirs
"I couldn't make myself any plainer if I'se a Quaker on his day off!" Shinn, The Music Man
"Nothing can be plainer than that ..." Penrose, a Treatise
"... but in the plainer and simpler kind of people, the deed of saying is quite out of use." Shakespeare, Timon of Athens
"But the longer I live on this Crumpetty Tree
The plainer than ever it seems to me
That very few people come this way
And that life on the whole is far from gay!"
Lear, Nonsense Songs
"Let an illustration make this plainer." James, The Meaning of Truth