“The extension of minds into the world through the use of artifacts was perhaps the last vital step in the evolution of culture that underlies the modern mind. Written symbols, alphabets and number systems, are ways of using the world to hold ideas. These external symbols allow a society a capacity for systematic thinking that would be impossible otherwise, a process we have referred to earlier as progressive externalization. Indeed, these external devices are not just static devices for memory storage. We have built external devices that process information, mirroring the process of thought inside our heads, at least loosely. Consider numerical calculation. You are limited in the amount of numbers you can easily add in your head. A paper and pencil increase this ability tremendously by letting you manipulate external symbols and hold intermediate steps in the calculation. By using artifacts that themselves process symbols, such as a handheld calculator, however, you can dramatically extend the realm of thought.”