We usually present Leibniz's argument in two ways: one is a more religious way (which is the original way), and the other is one that I think is less religious. But let's start in the most religious and primitive way.
<h1 class="pgc-h-arrow-right" data-track="2" > the original way</h1>
We can say that Leibniz's explanation begins with "God exists, and He is rational", and here is his argument for the existence of God:
The order and regularity of nature imply or point to a divine hand of creation, and imply that the existence of anything implies the necessary existence." Catherine Wilson, Stanford Encyclopedia of Philosophy.
Leibniz believed that the existence of God could be deduced from the highest concept of God, namely, the sum of all perfection. He then went on to say, "God is omnipotent and omniscient," and therefore, "God can create a different world or nothing." So he concluded:
God can choose to realize any world He wants, and achieving a world that is not as good as possible is inconsistent with His goodness.
If there is no best possible world, then God does not have enough reason to create one world and not another, so He will not create any world at all. But he did create a world, an existing world, so it had to be the best.
<h1 class="pgc-h-arrow-right" data-track="9" > Leibniz's optimism presents legacy problems in a less religious way</h1>
If we remove the traditional way of thinking about God from Leibniz's reasoning, focus on his rationalism, and apply Spinoza's concept of God (i.e., God = nature), this is how we understand what Leibniz is saying: there are many possible worlds, and they correspond to different laws of nature. If, then, the universal laws of logic are respected in the world in which we live, mathematics will make our world "the best of all possible worlds."
But would the laws of mathematics or logic be different in other possible universes? If you can answer this question and prove your point, you may win a Nobel Prize.
<h1 class="pgc-h-arrow-right" data-track="12" > how Voltaire responded to Leibniz's optimism</h1>
Leibniz argues that God doesn't have enough reason to create an imperfect world (mainly because God is a perfect and beautiful being, so he has no reason to make one world worse than another). Therefore, the world contains as much justice, goodness, and happiness as possible.
God does not roll dice. —Albert Einstein.
I don't think you should tell God what he should or shouldn't do – Nils Bohr.
Voltaire wrote a novel in response to Leibniz in 1759, The Honest Man. The novel is a direct attack on Leibniz's optimism. The novel begins with the young and naïve Gandhid, whose mentor Pangros instilled this optimistic philosophy in him. Pangeros claimed, "In this best world, everything is for the best results." But the young honest man was banished from the magnificent castle where he grew up and experienced war, hanging, earthquakes, cannibalism, slavery, and many other sufferings.
However, according to Leibniz's principle of richness, "a world with more diversity is superior to any world with less diversity." "Therefore, a world of both man and lion is preferable to a world of only man, regardless of the particular shortcomings of lions. Thus, even bad things may respect a set of necessary "perfect" things.
<h1 class="pgc-h-arrow-right" data-track="18" > the metaphysics behind Leibniz's optimism</h1>
Leibniz's argument is not just religious. There is a bigger perspective on how we should judge everything around us. Sometimes, for example, there may be benefits where we can't see; and, above all, since what we understand (so far) seems to be reasonable, our belief in knowledge, in science, may prove that we live at least in a perfect world.
At the end of the article, I would like to recommend this Voltaire's "Honest Man", which is a direct attack on Leibniz's philosophy.
Honest man ¥10.00 to buy