Leibniz is among the most eminent men in history—he invented calculus, he contributed to law, he contributed to philosophy, he contributed to history, the contributed to theology. Indeed, Leibniz is among the last polymaths—the list of fields he contributed to is vast (I’ve appended the Wikipedia list at the end of this article).
If we take hereditary factors as granted, what was his secret? Leibniz’s father died when he was young and left behind a large library—which the boy was technically barred from because it contained many “dangerous” theological tracts.
However, Leibniz attained access and worked his way through the library at his own pace—he read what interested him, dropped it when he wanted. He used intuition to move from one subject to the next.
This omnivorous reading schedule eventually crystallised into a desire to summarise all knowledge in one place—and it is no surprise that Leibniz joined an alchemical society later in life, he had a desire for “total knowledge” or “universal wisdom” (Hermetic).
So Leibniz’s method was that he used his intuition to read on whatever subject he liked for as long as he liked—and this included texts that were considered “dangerous” or “forbidden”. He was never forced through a curriculum, because by the time he encountered a curriculum he had already read through and around it.
Hence from a young age Leibniz had fully grasped the ancients, so that, as he put it, he carried their intellectual countenance as some men carry a suntan from warmer climes. Yet he had also read the Christian theologians—and contemporary thinkers such as Descartes.
The secret to Leibniz is that it all came from within, at his own pace and at his own discretion—and without any “censored” material to protect him, or a curriculum to restrict where his interests led him. He was a self-taught man—he was Hermetic, it all came from within.
It’s basically the opposite environment to our society where everyone is filtered through rigid bureaucratic systems that make you do things (pretend to learn things) whether you want to or not.
As an aside, Leibniz invented calculus at the same time as Newton—an event that led to much rancour, but surely must be providential (there’s a parallel to the way both Darwin and Russel developed evolution by natural selection at the same time).
The difference between Leibniz’s calculus and Newton’s calculus is that Newton’s calculus was very practical—the English are not a philosophical race, they are a mechanical race. Our intellectual innovations tend to serve particular ends (“common-sensical”)—hence Locke’s philosophy centres on epistemology and the basic question “what can we know in practical terms?”.
The Germans, by contrast, are a philosophical race. Hence Leibniz’s calculus is more about being an organic cohesive whole—it has a concern with what calculus means, not just what it does (Leibniz developed it, in part, because he really wanted to find a way to put metaphysical disputes on a basis that eliminated the ambiguities of natural language—as symbolic logic would later do).
Leibniz’s calculus is gestalt—in the sense that in gestalt psychology you grasp the whole field first, then the particulars. Newton gives you the particulars, whereas Leibniz wants to give you this elegant whole that delimits the entire operation. That’s the difference between a philosophical and a mechanical approach to life.