You could make the argument that English does not have singular and plural markers per se, but rather singular and "non-singular". (I'm not necessarily advocating this view, just throwing it out there.)
The evidence would be that the singular form is used to refer to one of something, while the plural form is used to refer to all other amounts. This includes everything between -1 and 1 (not including 1, of course).
- -25 volts
- -1 volts
- -0.25 volts
- 0 volts
- 0.1 volts
- 0.5 volts
- 0.999 volts
- 1.0000001 volts
- 1 volt
With that said, there are a few special cases that need to be addressed:
- There is no apple on the table.
- There are no apples on the table.
- There is half of an apple on the table.
While (2) might be more common, (1) is certainly possible in certain situations. This looks like an exception to the rule; note that (1) is normally said in response to an assertion that an apple should be on the table, while (2) is said in any situation.
Now, (3) might look like an exception as well, but grammatically speaking, apple is still referring to one apple, where "half of an apple" = "half of one apple" (logically and syntactically).