Just click on the blank comment field and type away. I would also comment on a comment with sincere gratitude, good or bad. I know it's hard to accept a bad comment, but I think if it adds to the article and furthers my knowledge then I would accept it. Now, there may be a comment that's just out of bounds, but you'll know it when you see it and I would still say thanks. For myself, HubPages is a learning experience as my writing skills leaves much to be desired.