This thesis describes a system that allows the designer of an interface between humans and computers to implement an English-like set of commands easily. Designers model commands on imperative English sentences containing verbs, direct and indirect objects, adverbs, adjectives, and prepositional phrases. The system restricts the ordering and presence command components as little as possible while still allowing the commands to be analyzed in a deterministic manner. Thus, commands formed with the system can mirror not only the form of English, but the flexibility of English as well. This system is based on the macro expansion of a command into a base language, and therefore has only the expressive power of the base language. Because of this, the system can only aid in the definition of commands, and not in the definition of a language. The language for describing the commands is structural in nature. The programmer defines the parts of a command instead of the syntax of the command. With each part of the command, the programmer defines sections of code that will be generated at various points during the recognition of the command. An implementation can execute generated code at some later time, at the end of the translation, or during the expansion. A prototype implementation expands of a file of commands into the VAX/VMS Digital Command Language. / M.S.