How to work around the missing cases of vis?

Question

The word vis does not have singular genitive and dative forms. This makes it difficult to use vis. (I was reminded of this difficulty by this Star Wars question.)

Can you suggest methods of working around the missing forms of vis when writing Latin? What should I do when syntax seems to require genitive or dative? The easiest way would be to use a substitute word for these cases or to coin new forms for vis, but both feel like a disservice to legibility and style. I am open to any suggestions.

For concrete examples, you can consider replacing robur with vis in the following sentences:

1. Terror roboris magnus erat apud senatores.
2. Haud multum roboris remanet.
3. Vir quidam roboris nuclearis peritus acroasem praeparaverat.
4. Marcum miseret roboris mei.
5. Roboris Marci causa abire constitui.
6. Haec potio magica robori meo prodest.
7. Caesar non pietati sed robori vivebat.
8. Voluntas robori dissimilis est.

Answer 1

Singular genitive and dative forms of vis exist but are very rare, according to the Gaffiot, which provides some examples:

Or in Calonghi:

So it may be possible to use those forms when needed (vis and vi).

Answer 2

To find the singular forms of vis is, I believe, fairly rare though perfectly valid. The more prevalent way of 'working round' is to use the plural, usually interpreted as 'strength', etc., though in either a physical or moral sense. The plural is found in all cases — except, of course, the vocative — and any good dictionary will give examples.

You might consider alternatives such as potestas and potentia, though care is needed to ensure that either is exactly apposite to the case in hand, rather as English speakers must choose precisely between puissance and pouvoir in French.

I wonder where you found your concrete examples using [robur], some of which have unusual syntax; are they, perhaps, your own constructions?

Answer 3

I realize that Sir Isaac Newton's Principia (v. Reference 1) is not part of the classical corpus, but he does talk quite a bit about vis in it, and he gives the word its modern definition.

From what I infer from reading the reference, he uses vis for the nominative and genitive, vi for the dative and ablative, and vim for the accusative.

Take a look and see whether you agree!