Five hundred years ago this week, a retired statesman wrote a book that changed the world. The statesman was Niccolo Machiavelli, and he had time to write because he had been deprived of office by the subversion of the republic of Florence by the aristocratic Medici family.

In a letter dated Dec. 10, 1513, Machiavelli described his life in retirement to a friend and former colleague. Mornings he spent attending to the business of his modest estate; afternoons, he spent in a local tavern, gambling and quarreling. But in the evenings, he wrote, he went to his study to read the history and philosophy of classical antiquity.

By means of those studies, he was able in his thought to “enter the ancient courts of ancient men” where, he says, he was “not ashamed to speak with them and to ask them the reason for their actions.” And he adds, “they, in their humanity” replied. (For the record, I’m quoting from the elegant translation of Harvey Mansfield, who was my teacher at Harvard).

The result of those studies, Machiavelli wrote in that letter 500 years ago, was a small book he had just completed, “The Prince.”

Even people who haven’t read it think they know what’s in it. The Machiavelli they think they know — the one whose name has become the epithet “Machiavellian” — is a teacher of evil and an enabler of tyrants. They remember that it is he, who in “The Prince” presents the odious Cesare Borgia as the exemplary statesman and who teaches rulers that it is better to be feared than loved.

Political evil was hardly new in the Italian Renaissance, though some princes of those times were unusually adept practitioners of that dark art. In fact, the catalogue of tyrannical and wicked rulers stretches as far back as we have historical records. Machiavelli was hardly the first to observe political evil, nor was he even the first to lionize its practitioners.

What defines the modern intellectual outlook is our embrace of another aspect of Machiavelli’s thought, one that we have absorbed so thoroughly we find it difficult to imagine there was ever another way of looking at things, namely his determination in his study of human behavior “to go directly to the effectual truth of the thing than to the imagination of it.”

The ancient and Christian writers about politics, he observed, “imagined republics and principalities that have never been seen to exist in truth.” They studied politics and the whole of human behavior on the assumption that there is an inherent moral order in the universe, and that we cannot even really understand human phenomena unless we also see them in the correct moral light.

On this view, one does not really understand tyranny without also recognizing that the rule of a tyrant is unjust, both oppressive to the ruled and destructive of the tyrant’s character and soul. To understand the politics of ancient Rome, according to Saint Augustine, was to see how it was based on a sinful pride, utterly foreign to the love of God that is the true principle of the city of God, in which we are all called to live.

Machiavelli, however, teaches us the opposite. Politics, he tells us, is not fundamentally about justice or goodness. It is about getting and using and keeping power. Power has its own rules, and these have nothing to do with morality. To understand power, he proposes that we focus on what works — the “effectual truth” — not on what might be or should be. And this is how modern political science proceeds even today.

In economics, we likewise study the “effectual truth of the thing,” assuming that the desire for economic profit, like the desire for political power, is natural and good.

Displacing the classical and Christian notions of virtue, Machiavelli writes that “it is a very natural and ordinary thing to desire to acquire.” Success is what we do and should praise; failure, not evil, is what we should and do blame.

Machiavelli frees us to celebrate tangible success, by relegating morality to the domain of imagination and opinion — something we argue and disagree about but which is not as solid or real as science, or profit or power.

To liberate ourselves from the seductive influence of Machiavelli’s thought requires only a single, but difficult thing: for us to study, as he did, the great ideas of his classical and Christian predecessors.

Joseph R. Reisert is associate professor of American constitutional law and chairman of the department of government at Colby College in Waterville.