The legal fate of Apple, Facebook, and Google depends on judges and regulators

As calls mount to break up big tech companies or limit their power, their legal fate will hang on how judges and regulators define their markets. "The social networking category" is a way to define this market that most readily casts Facebook as a monopoly. But if you call it "messaging," then Apple, Snapchat, and the cellphone providers all look like hearty competitors. Similarly, in many countries, Google looks to have a monopoly in the search market. But if you define the market instead as "online information," the case is a lot murkier. In tech, market definitions are unusually fluid because hardware evolves quickly and software is infinitely malleable. Lawsuits and antitrust cases move slowly, and in the time they can be tried, the markets tend to have mutated.