No `oxfordcomma=` optional argument? What will grammar pedants do? ;-)

More seriously, I might include the surrounding spaces in `last_word`, i.e. `last_word=' and ', so that people can use punctuation there if they prefer. I might also call it something like `last_conjugation` or `last_separator`. And I might also add a `sep=', '` option - though we can always leave that until there's a use case that actually needs it.