Imagine you are reading a story wherein members of a particular group are all named with Latin nouns for virtues or good qualities. (This is not simply a meta trick on the author’s part; the meaning of those names is acknowledged in-story. The setting is, however, a secondary world, wherein Latin is being used to fulfill a role more or less like it does in reality.) Most of the names are genuine third-declension nouns following the -tas, -tatis model — e.g. Pietas, Honestas — but a few are clearly adapted from first declension nouns so as to make for a consistent pattern — e.g. Justitas from justitia. The rest of the Latin in the story is grammatically correct.
Feel free to elaborate on your perspective in comments.