The German philosopher Gottfried Leibniz (1646-1716), one of the half dozen or so eminent philosophers treated in a new book reviewed here, has I think gotten a bum rap. For he is today known, if he is known, as the philosopher whose contribution to religious thought was famously, savagely, and effectively satirized by Voltaire in Candide. Dr Pangloss, one of the characters in that book, held that "this is the best of all possible worlds," and he persisted in this view as Voltaire subjected him to ever more convincing proofs, in the form of awful tragedies begetting unendurable human suffering, that it's not. Thus "Panglossian: characterized by or given to extreme optimism, especially in the face of unrelieved hardship or adversity."
The view that "this is the best of all possible worlds" was Leibniz's solution to the problem of evil. You know the puzzle. God, being merciful, must want to stamp out evil and suffering. And, being omnipotent, he must be able to do it. Yet the world is filled with both. Therefore, this merciful and all-powerful deity doesn't exist.
Leibniz escapes this trap by allowing that God is constrained by the same kind of logical necessities to which we all are subject. If p is true, then the opposite of p is false. If you choose p, then the benefits of the opposite of p are lost. This is as true for God as for everyone else. So you end up with this picture of the Creator very palely weighing the pros and cons of the various choices before him when designing the universe. "Human beings should be free. That means, however, that they might make poor choices that disrupt my beneficent plan. Okay, maybe I shouldn't let them do that. No, the consequences of that choice are even worse. I'll make them free." And so he proceeds through the cost-benefit analysis of all the decisions that he is obliged to make. At the end of the line, you are left with "the best of all possible worlds"--the key word being possible. It is easy to see that this amounts to a denial of God's omnipotence. It's also easy to see that it invites satire. And boy, did Voltaire ever walk through that open door!
One of the pleasures of satire is the enjoyable sensation that someone who deserves to get smacked is getting smacked, hard. As the effectiveness of the satire goes up, the stature of its object goes down. Candide, being highly effective, has left poor Leibniz languishing. But he is really at the other end of the spectrum from the bumpkin that readers of Candide may suppose him to be. I'm pretty sure that my account of his solution to the problem of evil isn't completely fair to him. Voltaire's critique is such a rhetorical triumph that everyone, including me, unconsciously understands the debate in his terms. When you know a little bit more about Leibniz, you are inclined to believe that anything that would occur to Voltaire would occur to him, too. Maybe there is more to the story.
For me, the proof of Leibniz's stature in the pantheon of the world's great geniuses is his work in mathematics. Years ago, I took "the calculus sequence" at the University of Minnesota. I still have the textbook. Ten chapters. Fall term, Calculus I, covered the first four. In the winter, Calculus II covered chapters 5 through 7. In the spring, Calculus III finished the book. My outcomes, as measured by the grades I received, were (as a calculus student might phrase it) inversely proportional to the effort I put into it. I aced Calculus I without working very hard. Calculus II began to be hard for me, and I worked diligently at it, eventually earning a B. Calculus III consumed my life for a couple of months, and I learned it, sort of, but it would be more true to say that things were moving too fast and I never firmly grasped the material: C. That was the last math course I ever took. I wasn't curious about whether the trend would continue.
My experience isn't unique. It's hard for most people to learn the calculus. If you know it a little bit, and were impressed by the effort it cost you, you're in position to esteem whoever first invented it--or discovered it, or developed it, or whatever is the proper term for bringing into use new mathematical techniques of considerable scope and utility. This achievement belongs to Newton and Leibniz, who, each working without knowledge of the other, invented ("discovered"; "developed") calculus. Newton's achievement may be credited to genius applied to certain problems that arose from his effort to comprehend physical reality--a new tool for a working scientist. Leibniz, however, was more or less a mathematical hobbyist. It's as if the calculus just fell out of his mind, the work product of pure thought undertaken for recreational purposes. That he should be known as the guy Voltaire beat up is an injustice that it seems a merciful and powerful overseer might have avoided.