It's a lie. Words serve multiple purposes, given their presence and arrangement. In formal writing-essays, speeches-diction should be formal. Formal: The man spoke to his father in a low voice so others could not hear.
And yet to me, what is this quintessence of dust? We complained about it. Formal writing can go to extremes when writers use jargon. However, if you are speaking with your friends, diction can be more casual-you may use informal words and even slang.
You ask Judge Thatcher; he'll tell you the same. The topic often determines the specificity and sophistication of diction. The patient has experienced acute trauma to the right femur, and must have surgery stat.
Informal: That guy told his dad secrets on the down-low.
Formal diction involves choosing words that are polite and proper.