For if a good speaker — an eloquent speaker — is not speaking the truth, is there a more horrid kind of object in creation?

Thomas Carlyle (1795-1881) Scottish essayist and historian

Speech (1866-04-02), “On the Choice of Books,” Inaugural Address as Lord Rector, University of Edinburgh
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Often rendered: "Can there be a more horrible object in existence than an eloquent man not speaking the truth?"

Regarding oration/declamation as an academic subject, and deemphasizing the importance of how something is said than what is being said.

See also Euripides (405 BC), Publilius Syrus (c. 40 BC).