I was wondering if it is grammatically incorrect to use "these ones" or "those ones" when answering someone who just asked me a question like.. "which ones are done?" or "which of those still need to be wrapped?" It seems to me that if it's ok to say "this one" or "that one" that "these ones" and "those ones" would also be acceptable. I notice I use them more often when I am pointing at something and want to be very specific.
The guys at work say that it is incorrect usage of grammar. Are they right?
They're right, but I don't think I can offer a clear explanation.
"These" is the plural of "this" and "those" is the plural of "that." It's perfectly OK to say "This one is mine; that one is yours."
But when we go to the plural, the "ones" is understood: "These are mine; those are yours."
Why this inconsistent usage? I wish I knew. English is full of rules, and half of them are broken.
Afterthought: I've just realized that the problem is with the number. You can say "This one," and "These two." If the number is uncertain, you can use "ones" in certain ways:
"Bring me four potatoes."
"Which ones?" [particular potatoes from a larger group]
"Those four in the bowl."
"No, they're too small. Try the ones in the cupboard." [the uncertain number of potatoes in the cupboard]
"Are these OK?" [we know how many are wanted]
"Those are perfect."