Re: when to use the word "fewer" instead of the word "less"
Simple.
18 eggs is fewer eggs than 24 eggs (as counted objects). 10 is less than 24 (as abstract numbers).
Similarly a dozen and a half turkeys is fewer turkeys than two dozen turkeys, but (etc.)
Alternatively, half a mile is less than a mile (not fewer) but to travel five miles is to travel fewer miles than to travel 10 miles.
Biting the hand that feeds IT
