Nonscientific survey here.
Question 1: In your own personal usage, can you use the word both with more than two items?
For example, do the following sound okay to you?
- Wash both the plate, the bowl, and the cup.
- Wash both of the three dishes.
Question 2: What about the word either? For example:
- Wash either the plate, the bowl, or the cup.
- Wash either of the three dishes.
Question 3: What about neither/nor? For example:
- Wash neither the plate, the bowl, nor the cup.
- Wash neither of the three dishes.
Question 4: What about whether? For example:
- Whether you open the door, close the door, or leave it alone, don’t go through it.
In my usage, all of those words apply only to exactly two items (though whether is a bit more flexible for me than the others), but recently I’ve seen several cases of more-than-two usage, so I’m curious about what other people think.
Various online sources suggest that the more-than-two usage is generally considered nonstandard but has been used by plenty of writers, especially in informal contexts. But even so, I’d be interested to hear about your usage.