Ambiguity and fear of ambiguity are common arguments for a variety of grammatical as well as editorial choices. For example, some people insist that since shouldn’t be used like because (as in “since you’re here so early, let’s build the trebuchet we’ve been planning”), because since could also mean “from that time forward”. The fear is that readers or listeners will commit to that latter reading and find it confusing — if not impossible — to switch tracks to the former reading.
Now, in the case of since, it’s actually rare that both meanings are reasonable for long enough to cause confusion; differences in the type of constituent or verb tense following the since tend to quickly disambiguate the sentence. But in other cases, ambiguity can be real and persistent:
(1) Since I was young, I went to church with my Mom [...]
In rare cases, the ambiguity can even be such that a reader can’t confidently determine which is intended, and in even rarer cases, the difference is meaningful. To insure against this confusion, some writers eschew the “because” meaning of since completely.
And that sounds like a good idea, except for one thing: there’s a flip side to the problem. So long as a substantial fraction of the linguistic community continues to permit the ambiguous form, it doesn’t matter whether you personally avoid the ambiguity; the ambiguous situation arises from unambiguous usage as well. In this case, it’s that ambiguity can arise even in the time-based usage of since:
(2) Since I was young, I have understood how right Benito Juárez, the outstanding Mexican patriot, was when he said: “Respecting others’ rights is the way to peace.”
Even if you never use the “because” meaning, your reader (probably) doesn’t know that. When they get to “Since I was young…”, they still might think that you’re using the “because” form. Again, this is probably only a temporary ambiguity. But it’s as much an ambiguous setting as the one that everyone complains about, so to avoid ambiguity, it also needs eschewed.
Here’s another example, from the cover of a book I’m reading:
The book is on Walter O’Malley, a former owner of the Brooklyn Dodgers, and the one who moved them to Los Angeles back in the 1950s. The front cover of the book, pictured above, reads “The True Story of Walter O’Malley, Baseball’s Most Controversial Owner, and the Dodgers of Brooklyn and Los Angeles”.
Now, if there were no such thing as the Oxford comma in this world, this subtitle would be unambiguous — baseball’s most controversial owner would clearly be an apposition referring to Walter O’Malley. (This is, by the way, the intended reading.) But because the Oxford comma exists, this could be a list. That’s the case even if neither the writer nor the reader ever uses the Oxford comma. The possibility of the Oxford comma will still color the interpretations.
I see two lessons here for usage in general. The first is that your writing and speaking do not exist in a vacuum. The principles of usage on which you make your usage decisions ought to take account of how other people use the language. It’s nice*, perhaps, if a writer insists that nauseous can only mean “inducing nausea”, but if no one else adheres to this rule, their readers probably won’t be able to recognize or use that principle in interpreting the writing. Common usage has an unavoidable influence on one’s readers and listeners.
The second is that ambiguity is not limited to contested usages. We tend to think of these debates about ambiguity as each influencing a particular choice or construction, but there’s almost always an overlooked construction that’s affected as well. If the fear of ambiguity is sufficient for a writer to avoid the ambiguous choice (e.g., the Oxford comma or because-since), then the fear of ambiguity also ought to cause the writer to avoid the ambiguity inducer (e.g., appositives in lists, time-since).
There are cases where that second avoidance is reasonable — I think I try to avoid appositives in lists, for instance — but in many situations, this would be tantamount to cutting the word out of the language. If both those senses of since are out, when could it be used? In cases like this, we really have to think hard about the intensity and importance of the ambiguity in the usage before deciding whether or not it’s tolerable. A blanket dictum against ambiguity is too broad a brush.
*: I’m, of course, using nice here in a sense somewhere between the rare “precise or particular in matters of reputation or conduct” and the obsolete “displaying foolishness or silliness” meanings.