This article presents a sketch for a theory of the rhetorics involved in categorisation and the creation of culture in online communities. Persuasion, or shaping perceptions of the world, is never incidental to social life, but living online necessarily involves persuasion as it is difficult to bring force to bear, although people can be temporarily excluded from different groups to different degrees, and the modality of persuasion may be influenced by the structures of communication in play. Communication almost always involves an attempted act of power aiming to produce a response in another. It is argued that linguistic categories, especially self-identity categories, are to some extent flexible, and that they exist in connection and contrast with other categories. The meaning of categories depends upon the ways they are framed (frames can also be categories), and framing and category content can be the subject of argument. Among the most important ways of framing online by Westerners are by space, public/private, authenticity, gender and community. The rest of the article explores the nature of online communication and power; how gender is used as a category; the kinds of effects that this categorisation has had; and how this category becomes salient within the framework of people making a "community" on the Cybermind mailing list. (Contains 15 notes.)