I have been writing my first project that I intend for publication, and as with older projects, I have been bouncing ideas off of people here and there when I am in a creative rut. But how much help does a person need to give me before I have to consider them a co-author?
I am not sitting down with these people and actively writing with them, it's more like generic advice. Things like sample questions to ask one's self about new characters in order to make them well-rounded and define motivations, or their feelings of interest based around the general plot.
My concern is that since I have only just started writing, and really haven't gotten stuck-in to the meaty bits, that there might come a time when I start asking people for help that should constitute a credit. I am not opposed to having a co-author(s), but I would like to know if there is any hard and fast rule about how much input one needs to have to be considered as a co-author.