Ward: What's the difference between Tropes and Figures? How to select the words?

Gresham College

John Ward offers a useful and straightforward distinctions:

"Tropes are chiefly designed to represent our thoughts, but figures our passions." System I, 384

These are embedded within styles (plain, middle, and grand) to mean that different subject require different literary treatments. See Howell, 115.

And then Howell, 96-97 nicely explains Ward's idea of how to select the "words" in a piece of writing or discourse: "...a writer in arriving at the content of his discourse would always need to consider his words in relation to

1. what they would announce about the subject under discussion, 
2. what they would reveal about the author doing the talking or writing, and 
3. how they would affect the audience of listeners or readers"

Howell, 97

Reference:

Howell, W. (1971) Eighteenth-Century British Logic and Rhetoric. Princeton