Q: I find the use of “or” confusing before the last item in a complicated list. For instance, “when shareholders have different consumption preferences, information, tax bases, or investment horizons.” Readers expect “and,” but have to stop and rethink the passage when they get to “or.” Why not put another “or” earlier in the series to help them?
A: We don’t find that passage confusing, but if we did we wouldn’t add an “or” to the series. An extra “or” would make the writing bumpy and might in fact confuse readers.
If you feel that series or another is hard to read, it would be better to add “or” before each item and delete the commas: “when shareholders have different consumption preferences or information or tax bases or investment horizons.”
If a writer (or speaker) believes that clarity requires repetition of the conjunction before each item in a series, then it should be repeated. The writer’s ear should indicate whether that would be helpful.
But otherwise the repetition isn’t required. Commas can be used instead. The only requirement is that a conjunction (“and” or “or”) be used before the final item.
Finally, as we’ve written many times on the blog, we believe a final comma before the conjunction is helpful.