Professor of mathematics at Temple University in Philadelphia
Thanks for your invitation (and for your project in general). I'd respond more fully but the question seems too ill-defined to answer. (I guess I still have something of the reductionistic, literal mindset of a mathematician despite periodic forays into more nebulous realms.) An invention or innovation that becomes essential has a tendency also to become invisible as we, in a sense, "grow around" it. If I were forced to name something, I guess I would go with Gutenberg's movable type. And if I wanted to be puerilely self-referential, my choice for most important invention might be the notion of a precise question. (Nevertheless, I do see the value of vague ones as well.)
