How we change what others think, feel, believe and do
Using style in an argument goes beyond simple statement of facts and description of reason and logic. Style moves an argument in to the realms of aesthetics, seeking to touch emotions rather than just intellect. Above all, it makes best use of language.
Eloquent language flows with an ease that belies the skill and artifice behind the delicate words. It uses subtle rhyme and alliteration to realize the alternative ways of presenting what could, otherwise, be a not so good way of saying this too well.
It uses devices such as reversal ('Ask not what your country can do for you; ask what you can do for your country') and triples ('for God, Queen and Country').
Powerful language selects individual words and combinations for their impact. It seeks to stimulate emotions through association with stirring themes. It may shock with brash images that threaten and trigger fear responses. It grabs you and forces you to agree.
Cicero was a military general who generally disapproved of emotions and thought they led to weakness, though it seems likely he would have been good at persuasion and making strong speeches that stirred the emotions. If you are going into battle, then emotional arousal seems like a good idea.
Appealing to emotions can be particularly effective, as these are always important in decision making, even when we are largely convinced by the logic of an argument. The point of decision happens when we feel that an argument is good enough. We close when our emotions change. Speaking with style multiplies the effectiveness of any argument.
In the original Latin text, this is 'elocutio'.