Leibniz's "Philosophical Optimism" or Sufficient Reason

Theodicy: the question of why God allows evil to exist or why He allows human suffering.

Popes' "An Essay On Man" (1733),  concludes that "WHATEVER IS, IS RIGHT."  This idea stems from the the brilliant and highly influential philosopher and mathematician Leibniz's so called "philosophical optimism".

Voltaire uses the character Pangloss to satirize both Leibniz and this type of optimism. 

Leibniz: (1646-1716). Before we allow Voltaire to satirize him, it's important to establish Leibniz's paramount value as a great and incredibly important Enlightenment thinker. As a mathematician, Leibniz, independently of Newton, invented or formalized Symbolic Logic, also known as calculus.  (Newton seems to have invented his method first and then told no one about it for twenty years.  However, his approach and methods are quite convoluted and difficult, and it is Leibniz's methods that are still used today.  The question both and many others were attempting to address was: how do you calculate the velocity of an accelerating/decelerating object at a specific, given moment.).

We also credit Leibniz with inventing a binary calculator that serves as the foundation of modern computers and he wrote all kinds of central science and economic stuff that is way over Tom's head. Basically, he was a genius, so let's be cautious with Voltaire's attack on this one element of his philosophy.

Although both men were devoutly religious, Newton famously limited his scientific findings to the physical world, while  Leibniz also argued that we could use symbolic logic to understand Godís creation -- the universe and man; Leibniz believed math/logic could explain God's will.  Like Plato and Aristotle, this difference between Newton and Leibniz marks an enormous split between two still competing world views.

Here is Leibniz's theodicy of "Optimism"  or "Sufficient Reason" in a nutshell, from Leibniz's Theodicy (1709): 

 Optimism: FORMAL LOGIC CAN BE USED TO UNDERSTAND GODíS INTENTION

            Premise: God created the universe*

            Premise: Godís creation is logically ordered (in the mathematical sense)

            Premise: God is all knowing and all good

            Premise: An all good god would only create a world with the minimum evil

            Premise: God could not create a perfect world because only God can be perfect

            Premise: Thus, this is the best of all possible worlds

 

            Conclusion: Optimism: Logic reveals the amount of evil (suffering) in the world is the very least amount: God created the best of all possible worlds.

(*Why Leibniz believes, logically, that God created the universe: All things or effects must have a cause. Yet one cannot trace the ultimate, original cause of anything back to nothing; thus: there must be an original cause of all things, the original cause is God. Or, the fact that there must be an original cause of all things proves the existence of God.)

(Also note how this argument is related to Descartes' argument for the existence of God:  An Evil Deceiver could make could make us confuse all "reality" with pure illusion (a la The Matrix) unless a more powerful, good God stopped him from doing so.)

In contrast with Locke, Leibniz isn't concerned with the world he observes but with the world his mathematical formula can prove; the entire plot of Candide suggests that the world we can directly, empirically observe does not match the mathematical formula: Leibniz blames our observations, and Voltaire blames the faulty logic: we trust logic over what we can all see and verify in the actual world.

 

So the philosophical concept being debated between Leibniz and Voltaire comes down to this: which should we trust more: logic (math: Descartes, Leibniz) or observation (experience, empiricism: Locke)?  This similarity and contrast between Leibniz and Newton is key: Both invented calculus.  Both believe formal logic could be used to unlock the secrets of God's so called Celestial Clockwork. Yet Newton incorporated formal logic with empiricism: close observation of natural phenomena.  Leibniz argues logic alone can determine that which is beyond observation. Voltaire is impressed with Newton's refusal to speculate on causes beyond those he can observe or prove. 

Good scientific reasoning, Voltaire would argue, is evidenced only when the two prove each other; if the observations don't match the formula, you haven't yet found the truth.

From this point on, philosophy, theology and science become three separate ways of thinking.  

For more than you want to know about Leibniz...