First Class on IRAC

Today we covered how to organize our writing for an office memorandum. I learned to use IRAC, which is issue, rule, application, and conclusion. The professor put a conclusion on the board, but I thought you started with the issue. Is the conclusion the issue? I was also confused about what goes into the rule. Do I describe cases or quote the law? I saw an example that had a discussion of the case, so that seems to be part of it. Is it the entire part of it?