John Backus

John Backus (1924–2007) was an American computer scientist best known for leading the team that developed Fortran — the first widely used high-level programming language — and for inventing the Backus-Naur form (BNF), the formal notation for describing the syntax of programming languages that became the standard for language specification.

Backus's work on Fortran at IBM in the mid-1950s demonstrated that machine code was not the natural language of computation. Before Fortran, programming was an exercise in manual translation: the programmer wrote mathematics, then translated it into assembly language, then translated that into machine code. Fortran automated the second translation, allowing scientists and engineers to write in a notation closer to their own thinking. The productivity gains were enormous, and the principle — that the level of abstraction should match the level of the problem, not the level of the machine — became the foundational argument for all subsequent high-level languages.

The development of BNF was equally consequential. In 1959, Backus adapted the notation of Noam Chomsky's context-free grammars to describe the syntax of ALGOL 60. The result was a meta-language — a language for describing languages — that was precise enough for compilers and readable enough for humans. BNF is now the universal standard for language specification, from programming languages to network protocols to data formats. It is the type-theoretic insight applied to syntax: the structure of a language can be described by a formal system, and the description can be checked for consistency.

Backus's greatest contribution was not Fortran or BNF but the demonstration that programming could be a science rather than a craft. He showed that the syntax and semantics of a language could be formalized, that compilers could be systematic rather than ad hoc, and that the machine was not the measure of the programmer. The persistent gap between programming as an engineering practice and programming as a mathematical discipline is a gap that Backus began to close — and that we have not yet finished closing.