Abstracting from the content of an argument reveals the logical form of the argument. The initial sections of this chapter show that logical form is the key to the validity of deductively valid arguments. The chapter then explores sentential logic, the logic of sentences. Finally, the chapter investigates the tricky terms only, only if and unless. To understand reasoning that uses these terms—in contracts and legal documents—many persons are forced to hire a lawyer. You, however, will be one step closer to becoming their lawyer.