Back in my youth of ancient days, somewhat after the invention of the wheel, but prior to the computer, English teachers introduced me to the principles of unity, coherence, and emphasis in communication. In simple terms, these mean:
(1) Talk about one thing at a time. (2) Organize your material so that one idea flows naturally into another. (3) Put the most important ideas either first or last, or both.
The reason I bring this up is that I’ve recently seen in close proximity two examples of otherwise good writing that violated these principles. The net result was jarring. To use a geographic metaphor, readers were jerked willy-nilly from Bangor to Bangalore without benefit of either a logical connection or a transition.
These are not new concepts, as my first paragraph hints. Here’s a link to a section from John Baker Opdycke’s work, Composition Planning. [See the third example, about 1/3 of the way down the page.] That short excerpt is one hundred years old, nicely written, and still worth remembering.
It should be noted that the three principles apply to writing at different levels: from the sentence to the entire piece, and everything in between.