What's about slugs?
If not, vine weevils (Otiorhynchus sulcatus) maybe the pest.
Control is possible with Methiocarb or Metaldehyde pellets (slugs) and Imidacloprid or nematodes (vine weevils).
Gerd Knoche. Germany

Paula,

No disrespect to my learned friend Gerd, but if it was vine weevil, I'd expect you to comment on the *edges* of the leaves being nibbled, but you don't...

ragged holes...
...hmmm...
if they were less ragged, I'd suggest leaf-cutter bees.
But I've never seen or heard of them going for violets (they go for maples in my garden).

The other holes that come to mind, re Viola, are those associated with shot-hole disease, a fungal problem where each spot starts, spreads, then the dead centre drops out. Those holes are more ragged, but not usually as large as you describe, in my experience.

If you can post a photo, that might help....

Thank you so much! I will try all the options. I have never seen slugs in my garden, but there is always the possibility that I haven't slipped on them yet.

I will take pictures when and if they appear, but I hope they don't!