Aristotle (384 BC – 322 BC) may well be the first person who formulated the four levels of discourse. At least I know of no sources that precede his Rhetoric and Poetics. They serve as the basis for many seminal works, such as Modern Rhetoric co-authored by Cleanth Brooks and Robert Penn Warren; more recently, The Elements of Style (50th Anniversary Edition) co-authored by William Strrunck and E.B. White and William Zinsser’s On Writing Well (30th Anniversary Edition).
I still have my copy of Modern Rhetoric (regrettably, now out-of-print) and it serves as the basis for EDNA, an acronym I devised years ago when I began to teach English at Kent School in Connecticut and have since discussed in hundreds of workshops and seminars conducted for corporate clients:
Exposition explains (exposes, reveals) with information.
Description makes vivid with compelling details.
Narration explains a sequence or provides a plot.
Argumentation convinces with logic and/or evidence.
Exposition is arguably the most valuable and yet least appreciated of the four. If used correctly and effectively, it offers great power to whatever you need to explain. These are among its most frequently used applications:
Analysis: Separate components (e.g. organizational chart, competitive marketplace)
Cause & Effect: Next to discovery, the single most important skill during process improvement initiatives
Classification: Organize what belongs where (e.g. division of labor, allocation of resources)
Comparison: Identify similarities (e.g. what sports and business share in common)
Contrast: Identify differences (e.g. how war differs from business)
Definition: Determine unique and precise essence (e.g. authentic leadership, core business, customer profile)
Note: Expository description provides objective details; description can also make effective use of figurative language such as “My foot’s asleep and it feels like ginger ale.”
The key point is that Exposition offers a variety of useful applications so the first question to be answered is:
“What specifically am I trying to accomplish with this explanation?”