When we say that something is ambiguous, we mean that it can be understood in more than one way. The word is built from Latin pieces that mean to move around, and so what we call ambiguous is something that won’t stay put long enough, so to speak, to make a commitment.
Take, for example, this brief sentence: He watched her play with pride. Imagine that the statement is referring to a father watching his daughter playing baseball. Can we say with certainty which of the two people involved, father or daughter, is acting with pride? We could conjecture, of course, that the sentence probably means that the father is watching with pride, because the idea that parents are proud of their children is a common assumption. But we could just as well conclude that the daughter is playing with pride, because of the energy and enthusiasm we often associate with youth. Ambiguity is moving about here.
Now language is not mathematics. Although we always have to be ready to move elements around so the reader will have a clear path to our thought, words and phrases and clauses do not always add up together with the severe correctness that 2 + 2 = 4, not 4.1. And that just means it’s all the more important to be aware of exactly where we are placing certain elements, particularly prepositional phrases like the one in our example. In finding the right place for an element, we are best served by the principle of proximity: elements that work together stay close together. And so if we apply this principle to our original sentence, He watched her play with pride, we can only conclude that the daughter played with pride, because the prepositional phrase with pride is taking its place immediately next to the element it intends to modify—and the principle of proximity keeps it there.
But if the writer had intended to say that he, the father, watched with pride, then the prepositional phrase should take its place elsewhere, again according to the principle of proximity: With pride, he watched her play. That revision, though, may seem to move in too literary a direction (and we would certainly fall off the expository cliff into poetry if we move the phrase around more violently: He watch with pride her play). So when we reassemble elements, but still don’t find the clearest, cleanest statement, yet another possibility always exists: to step into a different sentence structure entirely. If we transform our original simple sentence into a complex one, the father’s pride is secured: He watched her with pride as she played.
Writing clearly is all about commitment: we think hard about what we want to say, we discover, one revision after another, what was really behind that first hunch, and we do all that with an awareness of what confusions could arise in the way we are putting our sentences together. For we work to no one’s advantage—including our own—when we inadvertently sow doubt by writing ambiguously.