Last week I gave a paper at the Society for Phenomenology and Existential Philosophy meeting in New Orleans. It was on Nietzsche’ view of pessimism, so I thought I’d take the opportunity to talk a bit about the philosophical conceptions of optimism and pessimism.
Both optimism and pessimism are generally understood as involving an evaluation of life, whether it’s worth living or not; and that evaluation is typically tied to the experience of pleasure and suffering. That is, optimists weigh the pleasure that we can and often do experience in life against the pain and suffering that we endure and judge that, on the whole, pleasure generally predominates, such that the whole business is typically worth it. Pessimists, in contrast, judge that there’s more suffering than pleasure, and so life isn’t worthwhile.
Arthur Schopenhauer, a 19th Century philosopher, was a thoroughgoing pessimist. For him, life is essentially the struggle and striving of the drives and instincts within us, which he collectively calls “the will.” The will meets resistance in its efforts to find satisfaction, and that resistance causes pain and suffering (you want something, try to get it, something stands in your way, and that causes you to be unhappy). That state of dissatisfaction and its attendant pain is our common lot in life. We desire, and so we suffer. Any satisfaction of our desire is nothing positive; it’s merely a release from our temporary suffering. Further, any long term satisfaction soon turns to boredom. As Schopenhauer says in “On the Vanity and Suffering of Life”:
“…we have not to be pleased but rather sorry about the existence of the world; its non-existence would be preferable to its existence…”
A more extreme form of optimism was articulated by the early modern philosopher, Leibniz, who claimed that this is the “best of all possible worlds.” That’s a stark claim and for most of us, I assume, it seems like a real stretch of the imagination. Couldn’t the world be better than it is, if we, say, removed certain sources of unnecessary pain and added more sources of pleasure and happiness? According to Leibniz, no. He was compelled to adopt this idea because he was a theist, and he thought it impossible that God could’ve created a world that was less than absolutely perfect.
Voltaire makes merciless fun of this idea in Candide. The title character is persuaded to the Leibnizian view of things, but then witnesses a series of horrendous misfortunes, after each one of which he declares everything must be for the good, since this is the best of all possible worlds. The innocent Candide learns this theory from his teacher, Dr. Pangloss. Sometime after the latter’s apparent demise, Candide tells someone:
“A wise man, who later had the misfortune to be hanged, taught me that such things are exactly as they should be.”
Then, later, when he’s improbably reunited with Pangloss, Candide asks him whether he still maintains his optimism:
“Tell me, my dear Pangloss,” said Candide, “when you were hanged, dissected, cruelly beaten and forced to row in a galley, did you still think that everything was for the best in this world?”
“I still hold my original opinions,” replied Pangloss, “because, after all, I’m a philosopher, and it wouldn’t be proper for me to recant, since Leibniz cannot be wrong, and since pre-established harmony is the most beautiful thing in the world.” 
It’s a wonderful satire.
Further, in an essay called “On the Suffering of the World,” Schopenhauer argues that this doesn’t get God off the hook:
“Even if Leibniz’s contention, that this is the best of all possible worlds, were correct, that would not justify God in having created it. For he is the Creator not of the world only, but of possibility itself; and, therefore, he ought to have so ordered possibility as that it would admit of something better.” 
Since God created not only the world, but possibility itself, he ought to have created a better possibility than this one. Schopenhauer in fact goes on to argue that, far from being perfect, this is the worst of all possible worlds. He “argues” in “On the Vanity and Suffering of Life,” that if the world were just a little worse, it wouldn’t be able to exist. It’s not a very good argument, but Schopenhauer’s thinking is so dark and pessimistic that it’s fun to read.
Leibniz’s theory falls under the category of “theodicy,” which literally means the justification of God, or the ways of God. The problem is that there are contradictions and incoherencies in the way that we like to think of the Western God. For example, there’s a conflict between God’s being omniscient (all-knowing) and our supposedly having free will, the liberty to make decisions and choose the actions we’ll take; since, if God knows everything, then presumably knows what you’re going to choose, in which case, how can you be free to choose it?
But theodicy typically refers to what’s known as the problem of evil. That is, there’s a conflict between God as omnipotent (all-powerful), omnibenevolent (all-good), and the creator of the world. If God is the creator and all-powerful, then why is there evil in the world? If he’s omnipotent, then surely he could have created the world such that there would be no evil. You might want to say that evil is a result of the actions of human beings. That’s all well and good, but nonetheless innocents suffer whether at the hands of other human beings or from natural causes. And surely the avoidable suffering of innocents is itself an evil (avoidable because God could’ve prevented it, but he didn’t).
So theists like Leibniz, who strain for consistency in their thinking, are put in the position that the terrible things that happen, even to innocents, must somehow be for the good. They must be, since God couldn’t and wouldn’t have created a world that was less than perfect.
FYI, Nietzsche thought that theories that measured the value of existence in terms of pleasure and pain, like optimism and pessimism, were misguided:
“Whether it is hedonism or pessimism, utilitarianism or eudaemonism—all these ways of thinking that measure the value of things in accordance with pleasure and pain, which are mere epiphenomena and wholly secondary, are ways of thinking that stay in the foreground and naïvetés on which everyone conscious of creative powers and an artistic conscience will look down not without derision, not without pity.”
Pleasure and pain are ultimately unimportant; they’re superficial, and thus philosophies such as optimism and pessimism, which measure the value of the world in accordance with pleasure and pain, are themselves superficial.
 Arthur Schopenhauer, The World as Will and Representation, Vol. II, “On the Vanity and Suffering of Life,” trans. E.F.J. Payne (New York: Dover, 1969), p. 576.
 Voltaire, Candide, trans. Lowell Bair (New York: Bantam Books, 1959), p. 87.
 Ibid., p. 114.
Friedrich Nietzsche, Beyond Good and Evil, trans. Walter Kaufmann (New York: Random House, 1966), p. 225 .