There is a sense in which it is only at the end of a journey that you can actually begin it. You can only truly take it once you know what, exactly, you have been taking. Now that we are at the end of this one, we can look back over it, take stock, and see where we have come and, perhaps, something of what it meant.
We began with Descartes, who himself began again. He decided to restart his own education and, to whatever degree he could, to restart all of Western civilization along with it. He had received the best education available, yet he remained unsatisfied with it. Among his complaints, beyond its lack of certainty and its lack of practical utility, was the fact that he had not truly educated himself.
For Descartes, as for many philosophers, the only way one can genuinely know something is to learn it oneself, to arrive at understanding through one's own efforts.
That is what Methodological Doubt was entirely about. Descartes' whole project was to think through these questions himself, so that his conclusions would be his own beliefs: not beliefs he had simply swallowed, not beliefs taken on authority, not beliefs he held merely because everyone else held them, but beliefs he had genuinely examined, thought through, and made his own. In a very real sense, he was recreating himself. After all, if your body is what you eat, then your mind is what you believe.
Descartes' famous line, of course, is "I think, therefore I am." But we might reinterpret that as: "I think for myself for the first time, and therefore I am a genuine self now for the first time. Only now am I truly myself." He was unsatisfied with the world he lived in, so he set about making the world he wanted, and that is, in large part, the world we live in today: a world of jets, instantaneous communication, and open-heart surgery.
Descartes believed that there were, in principle, no limits on what we could do, because there were no limits on what we could know. We could know the fundamental structure of the universe. We could know the categories that everything falls into. We could know the very nature of God.
This is precisely what Hume objected to. Hume felt that Descartes did not understand the very thing he claimed to be doing, which was doubting. Descartes thought he could doubt his beliefs at will, when in fact we cannot doubt certain beliefs at all. We cannot doubt that the second billiard ball will move when the first strikes it, because our brain will expect that outcome regardless of what we consciously think.
All the conscious deliberation that Descartes went through operates entirely on the surface. The really important activity happens beneath our awareness, in what Hume calls custom or habit, a kind of hardwiring that is not susceptible to conscious control or change. It is not a belief in the ordinary sense, not something we arrive at through reasoning. It is something we simply are.
For Hume, this represents a limit we cannot get beyond, yet it is a limit that is not merely restrictive but enabling. It is what allows us to make use of past experience in ways that pure reason could not. If we were to become the purely rational thinking things that Descartes envisioned, Hume argues we would die immediately, because we could not sustain the habitual beliefs that guide us through our lives.
Where Hume objected to Descartes, Kant reconciles them. Kant salvages what he sees as valuable in each thinker and cuts away what he regards as mistaken, bringing together the two schools of rationalism and empiricism that had been warring for two hundred years, until they became a unified and coherent system in his philosophy. Just as Hume took Descartes' method of doubt and, in Hume's view, applied it more rigorously than Descartes had, Kant took Hume's insight that we impose concepts like causality onto experience and developed it further than Hume himself had managed.
Each of these philosophers takes ideas from predecessors and adapts, extends, deepens, and applies them in new contexts to improve upon them. This is the cumulative movement of the tradition: each thinker inherits a set of problems and tools, and hands them on transformed to the next.
This is how the history of philosophy works. It is a long, long conversation in which everyone tries to improve upon previous ideas by making them their own.
Nietzsche believed he could take Kant's ideas further than Kant himself had. We impose our concepts on experience, we suffer from transcendental illusion. Nietzsche accepted all of this, but pressed the point harder. Yes, we now have science, and we can do remarkable things, but what is the point if none of it matters? We can live much longer, yet we have nothing to live for. The very process that generated all this knowledge has been quietly undermining its significance all along.
We cannot go back, of course, and we cannot retreat. But we can move forward. We can take seriously the transcendental illusion that Kant identified and recognize that we are the ones doing the organizing. We are the ones generating the ideas we mistakenly believe exist outside of us, and the most important of these are the values by which we live.
We tend to think our values are handed down to us by God, or that they exist objectively out there in the world. In fact, we have been creating them all along.
This initially fills us with horror, because it seems paltry. It seems as though it cannot be enough, given that we are so accustomed to the idea of objective values. But if we go all the way through that nihilism, through to the other side, we can realize that this is the salvation. We can realize that our ability to create values, which is what we have had all along, is precisely what enables us to create new ones: better ones, ones that are faithful to the Earth instead of to some transcendent deity, ones that will make life better instead of demeaning life in favor of the afterlife.
This is what Nietzsche tried to dedicate himself to, because he believed that our greatest strength is our creativity: our ability to always come up with new ideas, new values, and new avenues to explore, rather than to remain at home. Kant wanted to make a home for us. Nietzsche wants to go exploring, to see what else is out there.
For Nietzsche, we are the animal that has no limits, the animal that goes beyond whatever limits it finds. Evolution is our true creator, rather than God. The single-celled amoeba that begins life could not conceive of what it would be like to be a fish, which is where it eventually ends up. It could not imagine what life would be like in that form. And the fish could not comprehend what it would be like to walk on the surface of the Earth and breathe air, and the land-dwellers had no idea what it would be like to take flight.
None of them could have the faintest inkling of what it would be like to be an animal unrestricted by evolution, unbound by instinct, an animal able to turn around and comprehend the very process that led up to its ability to comprehend that process, and then to control it. This drive to surpass what we have been, to be more than what we are, is what we are. It is our essence to be more than any essence we find ourselves to be.
This is how the history of philosophy has worked. This is how we have seen every thinker react to the previous thinkers, and this is what you have done in your own life. You started out as a single-celled being, then you breathed liquid in the womb, then you crawled on land, and then you became a thinking being. Through this process of thinking, you have fundamentally changed yourself over and over again.
Think of who you were as a fifteen-year-old. Your fifteen-year-old self could not have made the choices you make today. That self had radically different values, saw the world in a completely different way, and made choices according to entirely different principles than the person you are now. Your fifteen-year-old self could not have recognized some of the thoughts you now have, could not have thought them, could not have seen the value in the values you now take to be defining of your life.
You have become a completely different person. And your ten-year-old self could not have recognized their fifteen-year-old self. Between the ages of ten and fifteen, if you passed through puberty, you practically became a different species. You developed a whole new sense and saw an entirely new dimension of the world. You have been changing species throughout your whole life.
If we can take that backward-looking view and turn it toward the future, the question becomes: who will you be? Who can you be? What are your limitations? That is the question Hume and Kant asked. What will you do to overcome those limitations? That is Nietzsche's question. Kant wanted us to grow up; Nietzsche wants us to never stop growing.
Nietzsche wants the you five years from now to be unrecognizable to the you today, just as the you today is unrecognizable to the fifteen-year-old, and the fifteen-year-old to the ten-year-old. He wants you to keep evolving, keep growing, and never to hold a constitutive view of yourself, the sense that you have finally become who you really are. Instead, he asks you to hold a regulative self: Who can you become? What else is out there? What new thoughts can you have?
I hope that thinking through these four philosophers has opened up your horizon, at least a little, into the possibilities of what else you can think. I hope you continue exploring.