Telescopes – or even anything with lenses – are clearly extensions of the power to see, and television also extends the power of hearing in the same way. Assume all the other senses could be extended the same way, allowing us to taste things in other countries, smell things on Mars, feel the texture of moon rocks, etc. A man might have all his senses extended in this way, and so while sitting alone in a room might sense anything in the Cosmos. Then perhaps by accident or overuse the pads of the fingers might become damaged, and we might bypass the skin in his fingertips and tie the tactile machine into nerves that are deeper down. The tactile machine is now an extension not of the finger pads but of deeper nerves.
We can see where this is going: all the technology and machinery of sensation might be tied to deeper and deeper nerves and become extensions of powers of a more and more whittled-down man. But for all that – and this is the crucial point – the technology is still and extension of human power. No one knows where the limit of this extension is reached: perhaps we need a brain, perhaps only a single cell, but there is a limit to this invasive, downward extension. “Machines all the way down” means the machines cease to extend a power, and therefore technology would cease to be technology.
Objection: This assumes that we can know the definition of technology a priori in such a way as to recognize that it is essentially an instrument. But this is a purely a posteriori matter. All we can do is replace all the parts of a man and see what happens. Maybe he’ll be a man after all that, maybe he won’t, but we can’t just define the answer into existence.
Response: But we can know the definition and essence of technology a priori: it owes its very existence to our choice to make it what it is. Technology has no formal existence outside the one we will it to have. If I need a utensil to flip pancakes, and either make one or stipulate that some object will count as one, then it is impossible for me to be mistaken about the nature of the thing qua pancake-flipper. It might, of course, be a dreadful or failed or ill-considered flipper, but I can’t be confused or mistaken about what it is.
This provides an interesting new point of view to the brain-in-the vat thought experiment. Seen from this angle, it is a proof of the primacy of life in experience. We need a brain in the vat, and to replace that brain with chips and switches does not change the need for the organ. In the BIV, we have the brain and its technological extension, but if we replace the brain with chips and switches, we simply make it a technological extension a brain other than the one in the vat.