The Rules of Eloquence are True, Though Sometimes Used to Persuade Men of What is False
54 There are also certain rules for a more copious kind of argument, which is called eloquence, and these rules are not the less true that they can be used for persuading men of what is false; but as they can be used to enforce the truth as well, it is not the faculty itself that is to be blamed, but the perversity of those who put it to a bad use. Nor is it owing to an arrangement among men that the expression of affection conciliates the hearer, or that a narrative, when it is short and clear, is effective, and that variety arrests men's attention without wearying them. And it is the same with other directions of the same kind, which, whether the cause in which they are used be true or false, are themselves true just in so far as they are effective in producing knowledge or belief, or in moving men's minds to desire and aversion. And men rather found out that these things are so, than arranged that they should be so.
Source: Christian Doctrine (New Advent)