Turing's "On Computable Numbers"

In “On Computable Numbers, with an Application to the Entscheidungsproblem,” Alan Turing describes a theoretical device – the Turing machine – capable of executing any algorithm that can be expressed as a finite set of rules. He uses it to prove that certain mathematical problems are undecidable: no machine can solve them in finite time.

The paper is foundational to computer science not because it builds a machine, but because it defines one. It also implicitly raises a question that will recur across the history of AI: if a machine can execute any finite procedure, what is the relationship between procedure and thought?

Source: Alan M. Turing, “On Computable Numbers, with an Application to the Entscheidungsproblem,” Proceedings of the London Mathematical Society, s2-42(1), 1937, 230–265.