Imagine you are helping to design a new space shuttle for NASA, and in the course of the work you need to evaluate
y = 5 + 4 × 2
The question is this: Which operation will you perform first? Will you add first? In which case you would find
y = 9 × 2 = 18
Or will you multiply first? Then you would obtain
y = 5 + 8 = 13
The difference between 13 and 18 could be crucial to the success of a shuttle mission. For example, if the calculation applies to a life-support system, the error could jeopardize the crew.
Fortunately, arithmetic has rules for resolving our dilemma. The applicable rule here is that higher-order operations take precedence over lower-order ones: we must multiply first, then add, and the correct answer is 13. Mathematics provides rules to prevent ambiguity when we need to interpret a mathematical sentence (an equation).
In an exactly analogous fashion, language has rules of good usage that prevent ambiguity when we need to interpret an English sentence. But the writer must invoke those rules if the reader is to be informed rather than confused.
Sense and nonsense are distinguished, in part, by the relative ordering of elements: verbs, subjects, main clauses, subordinate clauses, prepositional phrases, sentences themselves. Consider this example (No, I didn't make this up.):
Figure 1 shows measurements of the water level as the tank is being filled with error bars.
The rules of good usage make a substantial contribution to a clear technical style, and as Edward Tufte has emphasized : style matters. A vague, convoluted, opaque technical style signifies a writer who places little importance in either the writing or its readers. Consequently, the writer loses credibility and, sooner or later, readers will be forced to guess what the writer is trying to say. And in technical writing, it is as wrong to force the reader to guess meanings of sentences as it is wrong to force the reader to guess numerical results from equations. The consequences of misinterpreting a sentence in a technical document could be just as disastrous as misinterpreting an equation—just as disastrous and just as unnecessary. Garbled writing is a product of garbled thinking, and our society cannot afford garbled thinking about technology—either from those who develop the technology or from those who use it.
[ 1 ] Edward R. Tufte, The Cognitive Style of PowerPoint: Pitching Out Corrupts Within, 2nd ed., Graphics Press LLC, Cheshire, CN, 2006.