Turing's present-day and all-time relevance arises from the timelessness of the issues he tackled, and the innovative light he shed upon them. Turing first defined the algorithmic limits of computability, when determined via effective mechanism, and showed the generality of his definition by proving its equivalence to other general, but less algorithmic, non-mechanical, more abstract formulations of computability. Turing also first implicitly introduced the perspective of 'functionalism'—though he did not use the word, it was introduced later by Putnam, inspired by Turing’s work—by showing that what counts is the realizability of functions, independently of the hardware which embodies them. No one to this day has invented a computational mechanical process with such general properties, which cannot be theoretically approximated with arbitrary precision by some Turing Machine, wherein interactions are to be captured by Turing's innovative concept of oracle.
From Philosophy to Computational Logic: Festschrift in honour of David Pearce's first 60 years
