Zadig has been called a philosophical novella—and for good reason. Strung throughout the episodic story are a series of parables that teach lessons about ethics and morality. In most cases, it is the story’s protagonist, Zadig, who is teaching. Zadig teaches verbally, often through parables, allegories, and analogies to show other people a different way of thinking about things. He does so in a poetic manner, using allegorical examples and subjects. And at the same time, Zadig employs a keen intelligence to discern the truth, using what later will be known as the scientific method to see and reveal what other people cannot see.

Zadig is fined and tried early in the novella for knowing something by his judgment that he has not actually seen with his own eyes. Zadig applies his brilliant mind to prove the existence of a horse and dog at a scene, using the physical evidence they have left behind to infer their earlier presence.

As I was walking down the Lane by the Thicket-side, I took particular Notice of the Prints made upon the Sand by a Horse’s Shoes; and found that their Distances were in exact Proportion; from that Observation, I concluded the Palfrey gallop’d well. In the next Place, the Dust of some Trees in a narrow Lane, which was but seven Foot broad, was here and there swept off, both on the Right and on the Left, about three Feet and six Inches from the Middle of the Road. For which Reason I pronounc’d the Tail of the Palfrey to be three Foot and a half long, with which he had whisk’d off the Dust on both Sides as he ran along.

Many later writers, including Sir Arthur Conan Doyle and Edgar Allan Poe, point to Voltaire’s Zadig as an inspiration and influence in the development of their own literary detectives.

When burdened by the weight of extra supplies taken from the camels, Zadig tells his master about the simple physical law of gravity. (This was a physical law that the French were slow to accept, for which Voltaire often criticized the French.)

Zadig took the Liberty to explain the Reason thereof; and convinc’d him of the Laws of the Equilibrium. The Merchant was a little startled at his philosophical Discourse, and look’d upon him with a more favourable Eye than at first.

When Zadig visits the languishing, sick Prince Ogul, the prince is having his servants look for a basilisk to cure him. Zadig tricks the prince into instead practicing daily exercise, staying sober, and using a medicine bag. This cures the prince, who continues to change his lifestyle.

Zadig teaches his Egyptian master, Setoc, how to recover a debt without having any proof of the indebtedness. The money has been counted out to the man on a large stone, and he tricks the man into admitting he knows where the stone is.

Setoc loves the stars in the sky because they are so brilliant and so far away. Zadig lights a number of candles in a room and sits and adores them while Setoc is there, ignoring Setoc. Setoc understands from this that it is the maker of the stars he should adore, not the stars themselves, a critique Voltaire is making toward the idolatrous adoration of images by Christians.

In Setoc’s land, there is an ancient practice of the burning of widows on their husband’s funeral pyres—the rite still exists merely because it is ancient. Zadig argues that this is ruinous for the women and for the state and convinces Setoc and a court of judges to amend the old law so that the widows spend a few hours with a young man, chatting, before they decide to immolate themselves on the pyre. Flirting with the young men, the women will usually realize they have more to give to life and decide to stay alive instead.

Voltaire celebrated a mix of earthy humanism and rational thought throughout his life, yet he did not entirely reject spirituality, as long as

a religion . . . makes one great family of all men, and whose practices are founded on tolerance and good works.

This may explain Zadig’s eventual submission to Providence, as he bows to the lessons taught to him by the angel.

In one episode in the novella, Zadig speaks to the various sects of Bassora, each of whom has proclaimed that their religion is the supreme religion. Zadig tells them that they are all agreed—they are all right—without knowing it.

In his day, these opinions did not open doors for Voltaire and would probably not do so even today, as it is the rare religion that espouses that all religions are the same.

Even in the episode with the angel Jesrad, the story of Zadig is akin to the biblical story of Job. Zadig is visited by trial after trial in this life, and his faith is tested. He more or less passes the test by keeping his faith and continuing to live a moral life. The angel says absolutely nothing about reward or punishment in the afterlife—these trials are all about this life.

The Wicked, replied Jesrad, are always unhappy. Misfortunes are intended only as a Touch-stone, to try a small Number of the Just, who are thinly scatter’d about this terrestrial Globe: Besides, there is no Evil under the Sun, but some Good proceeds from it.

Voltaire thinly disguises himself as the Persian poet "Sadi" in the dedication of the book. Saadi Shirazi is best known for Bustan (The Orchard) and Gulistan (The Rose Garden), two books of poetry. Bustan is told in epic verse and contains stories illustrating the morality and virtues of Muslims. Gulistan uses anecdotes and poetry to offer advice and reflections on human existence. Shirazi is also a strong humanist who says,

If you are indifferent to the misery of others, it is not fitting that they should call you a human being. . . . The example of the believers [Muslims] in their affection, mercy, and compassion for each other is that of a body. When any limb aches, the whole body reacts with sleeplessness and fever.

Saadi’s belief in one large human family, intensely connected with one another, mirrors Voltaire’s belief in “one great family” of humanity. In fact, in his intimate circle, Voltaire enjoyed being called “Saadi” by his closest friends. “Saadi” and “Zadig” are fairly similar names; they are both Voltaire in this book, demonstrating the author’s thoughts, beliefs, and deepest philosophic convictions.