To be honest, I struggled some with Miller, but I am going to try and suggest what I think she was driving at in regards to the concept that genre is based in social action. She states something quite appropriate: “…for genres change, evolve, and decay; the number of genres current in any society is indeterminate and depends on the complexity and diversity of society” (p. 163). This makes sense, if, in fact, I am getting her point. The more advanced or privileged a society is the more genres they will have. If North Koreans are banned from the internet, then they lack the ability to use a blog as a genre of writing. Writing blogs happen on the internet, and if you do not use the internet, you cannot write in that genre. The inability to use the World Wide Web prevents some from taking social action in a certain genre. Blogs may be very foreign to the North Koreans, assuming they have no or quite limited internet access. If I do not know how to use Instagram, I cannot use that genre to express myself. The ability to act with certain media may promote the use of certain genres and inhibit use of other genres.
Furthermore, I could post my thesis of George Whitefield on Facebook, but it is likely no one will read it. Instead, I could post a quick note saying, “Just finished my thesis on Whitefield. So happy!!!” That may get 30 “likes”. The medium of Facebook dictates what genre I will use. The medium I choose affects my actions which in turn affects my genre of choice. Some genres are better left far from certain media, just as I highlighted with my thesis and Facebook. Miller writes further, “Genre refers to a conventional category of discourse based in large-scale typification of rhetorical action, [genre] acquires meaning from the social context in which that situation arose” (p.163). I think this is quite accurate. We are limited by some media as to what we can do. One would not post rather emotional love poem to his wife on Facebook. It would take away so much of what should only be said in private. I suppose I would argue that the medium used (which is intrinsically tied to social action) dictates genre. If I can send email, I may be more casual, than if I am writing something to be delivered via a sail boat to England.
To close, when we are writing we must always be aware of the medium we use. Some media require and demand more academic precision. Some demand less. I would argue that when we write public, the medium controls our social action which controls our genre. There are obvious way different styles between different media choices. A speech in congress is going to be inherently different than a goofy YouTube one shares with friends. The medium affects the action which affects the genre.