I have been teaching about legal reasoning and legal argumentation for years. When I do so, I try to impress upon students that legal argument is both simple and complex.
It is simple because in every legal case there is, in essence, one basic type of argument at the core of the dispute between the parties. This argument works from a general legal rule to a conclusion about the application of that rule to a set of facts. Philosophers and logicians would say that the basic form of legal argument is a syllogism: a simple three-step argument involving a major premise (a general principle or rule), a minor premise (a claim about a particular case or scenario) and then a conclusion (an application of the general rule to the particular case).
Here is a simple conditional syllogism: