This is the first in a projected three-part series about the law of the excluded middle, a (disputed) logical principle according to which, for any well-defined proposition, either the proposition is true or it is false. Today I will explain the law in question and offer a classical argument for its validity. On another day (not tomorrow, I assure you): I will explain why I do not believe that argument is a strong one and why we might want to allow for violations of this LEM. When I get around to Part III, I will discuss how the dispute feeds into political philosophy and certain questions about the legitimate regulation of markets. So ... let us proceed. When it seems that a proposition IS both true and false, or is neither, and in either case is in violation of this law, various remedies are available: the proposition in question might just be nonsense (as for example the claim that the Jabberwocky has a frumious Bandersnatch), it might embed a false premise (as for ...