More than any other political theorist, Machiavelli's reputation precedes him. Some people talk about Rawlsian ideas or Kantian ethics or a Hobbesian world – usually those who want to sound clever and educated – but it's perfectly fine to use the word Machiavellian without claiming to have read The Prince. Everyone does and everyone knows what it means.

It can come as something of a surprise, then, to find that Machiavelli wrote in The Prince that "a man who becomes king … must make it an absolute priority to win over the affection of the common people", or that "sensible rulers and well-run states have done all they can … to keep the people happy and satisfied; indeed this is one of a ruler's most important tasks."

The ideal ruler is not, it seems, a dagger-wielding psychopath. On the contrary, he "should go about things … humanely". Nor should he be a leader in the sense of inspiring terror in everyone around him. On the contrary, "a king must guard against being despised and hated", both by noblemen and commoners.

Noblemen, or at least some of them, must feel comfortable speaking honestly to their prince. A leader who "trusts no one makes himself unbearable". Accordingly, "he should make it clear that the more openly [ministers] speak, the more welcome will their advice be".

Respecting commoners is, if anything, more important still. "People's aspirations are more honourable that those of the nobles," Machiavelli admits. Therefore, "a ruler must avoid any behaviour that will lead to his being hated or held in contempt".

This is more than hot air. It means that the ruler should "respect" the "guilds and districts" into which "every city" is divided, and "go to their meetings from time to time, showing what a humane a generous person he is". It means that "if he really has to have someone executed, he should only do it when he has proper justification and manifest cause".

And it means that he should instate and protect sound public institutions. France, he says, is a one of the better governed states of our age, "full of good institutions", the most important of which is "parliament and parliamentary authority". "There couldn't be a better or more sensible institution," he gushes, "nor one more conducive to the security of kind and the realm."

None of which sounds particularly "Machiavellian".

It will be clear the Machiavelli's model prince is no political Satan, bidding "evil, be thou my good". Indeed, were he to have been so, he would, paradoxically, have been less shocking and somewhat easier to deal with. Monsters, after all, are manageable. Remorseless sadism may nauseate us but if we can convince ourselves that such people are completely different from us, not even of the same species, we do not feel quite so threatened by their actions.

By contrast, it is precisely because its model prince is recognisably human, valuing many of the things we value, and pursuing paths that we ourselves would advocate, that The Prince is so disturbing. He is one of us, too realistic, too credible to be readily dismissed. You may not always admit so in public, Machiavelli whispers to us, but you too think like this, don't you?

Machiavelli's moral universe is not one of unredeemed or unredeemable immorality, therefore. It is subtler, more amoral than immoral. By all means, govern well, execute sparingly, respect institutions, and invite honest advice, Machiavelli says, while in the same breath telling the prince that he must execute some of the coldest and most brutal acts of political violence.

So, for example, he reports that there are three ways of keeping control over newly conquered but previously self-governing states: "Reduce them to rubble … go and live there yourself … let them go on living under their own laws … and install a [puppet] government." Each has its own merits but "the truth is that the only sure way to hold such places is to destroy them". That isn't mandatory. You may decide not to raze them, in which case "the best way to hold a previously self-governing city it with the help of its own citizens". But it is still an option.

Machiavelli doesn't advocate violence for its own sake. On the contrary, he repeatedly insists that such frenzied aggression is counter-productive. What is shocking is the way in which the brutal rubs shoulders with the benign, the vicious with the virtuous in a matter-of-fact way. He is not so much saying the morally wrong way is the necessarily right way for a prince to go about his business. Rather, he is implying that the morally right way is simply irrelevant. What matters is staying in power.

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