How well do you know your discourse community?

Writers are often told to consider their writing audience and purpose but what does that mean? What it really means is understanding the discourse communities we write for because each discourse community has specific purposes and goals -- the reasons that communication takes place and the goals that communication should achieve -- but even more important every discourse community has rules and expected behaviors. Not following those rules (which are often unspoken and simply "known" by members of the community) will immediately mark you as an outsider or newcomer and diminish your credibility within the community.