I just found this on the net;
In English many such words have both a singular and plural form.
The plural form is used when one wishes to express a specific idea. For example, We have many chickens in our backyard.
The singular form that does NOT have a plural form, is used for a general idea. Such as: Tonight we ate chicken.
Source(s):
I'm have an English Degree but have forgotten much of it.
Perhaps this clouds the water a bit more.
Regards Hammer


