As a cognitive linguist whose job is to study conceptual systems, both conscious and unconscious, I was struck by what was meant by "invention."
• The most concrete "inventions" proposed have been gadgets, mechanical or biological — the printing press, the computer, the birth control pill.
• A step way from the concrete specific technical innovations are specific technical inventions of a mental character: Gödel's Theorem, Arabic numbers, the nongeocentric universe, the theory of evolution, the theory of computation.
• A step away from those are the general innovations of a mental character in specific domains like science and politics, e.g., the scientific method and democracy. I would like to go a step further and talk about the invention that was causally necessary for all of the above:
• The most basic fully general invention of a mental character is The Idea of an Idea.
THE IDEA OF AN IDEA
It's a bit more than 2,000, more like 2,500 years, at least in the West. It is an 'invention" in the sense that human beings actively and consciously thought it up: to my knowledge, it is not the case that every indigenous culture around the world objectifies the notion of an idea, making it a thing that can be consciously constructed.
What is required for all other human inventions is the notion that one can actively, consciously construct new ideas. We take this for granted, but it is not a "natural" development. Three-year-old children have lots of ideas and even make up new ideas. But they do not have the Idea of an Idea that they can construct anew; they do not naturally arrive at the idea that making up new ideas is something people do. The Idea of an Idea is a cultural creation that children have to learn.
It is only with the Idea of an Idea that we get conscious specific intellectual constructions like democracy, science, the number system, the computer, the birth control pill, and so on. The Idea of an Idea is the generative notion behind the very notion of an invention and is causally necessary for all specific inventions.