While Voltaire had many of the philosophical credentials of his fellow Enlightenment philosophers—namely, a belief in the power of reason, the importance of independent thought, and the rejection of religion as the sole bearer of truth—his perspective was somewhat less rosy. In Candide, Voltaire fleshes out his unique, and somewhat more pessimistic, perspective on human nature through the use of cutting satire.
Optimism was central to Enlightenment thinking, as philosophers believed that happiness could be achieved through human thought and action. In other words, the goal of life was not to achieve happiness on another plane but rather to achieve happiness in the present. Voltaire's Candide undermines that idea entirely though the satirical character of Pangloss, the optimistic philosopher.
Many Enlightenment thinkers believed that society should be governed by the "general will" of the people, usually through direct democracy. In Candide, Voltaire creates characters who are generally untrustworthy and often cruel, as readers can see in the way Cunegonde is treated. If people act like this, Voltaire intimates, perhaps they shouldn't be trusted to govern themselves. This pessimism about human nature goes against the belief of fellow Enlightenment thinker Jean-Jacques Rousseau, who believed that humans are inherently good.
Even so, Voltaire also satirizes a wholly pessimistic view of humankind through the character of Martin. While Martin seems to exemplify Voltaire's dark view of human nature, in reality, Martin's failure to learn and change based on his personal experience—a tenet of Enlightenment thought—proves that pessimism, like optimism, is worthless if it's not tempered by its opposite.
Voltaire demonstrates this through the character of Candide. While he initially is taken in by Pangloss's optimistic philosophy and finds common ground with Martin in his pessimism, Candide eventually moves past both into a more nuanced middle ground. In other words, Candide is the truest example of an Enlightenment figure—he learns from experience, rejects false authority, and comes to the conclusion "that we must cultivate our garden," relying on ourselves to find peace, not on systems of philosophy or religion.