In his book Against Democracy (2017), Jason Brennan presents a formidable amount of empirical evidence to the effect that the more someone is involved in politics, the worse he or she becomes as a person.

• The more you are involved in political debate (especially as the representative of a group or ideology), the less likely you are to reach reasonable conclusions. Participation increases people’s tendency to ignore facts that don’t support their position, to argue in manipulative and deceptive ways, to adopt extreme views, and in general it makes people more biased and less reasonable.

• The more active you are in politics, the less likely you are to talk with people whose views run contrary to your own. In fact, you may reach the point where you are unable even to imagine a point of view other than your own. As a result, the more active you are in politics, the less good you will be at doing what politicians are supposed to do: see enough sides of an issue to craft and sell a compromise.

• Ergo, people who follow political debate tend to be ignorant of relevant facts and inexpert at reasoning correctly about what they do know. But the situation among those who do not participate in politics is no better. The vast majority of the electorate know next to nothing about politics, and much of what they think they know is wrong.

• Since people who vote are people who take at least some interest in political debate, and since people who take part in political debate tend to be even more ignorant, biased, and unreasoning than those who don’t, those elected to office are likely to be incompetent or worse. To the extent that the quality of our government affects our daily lives, those who participate in politics are diminishing our quality of life.

This is what Brennan makes of the evidence, anyway; some say that the studies he cites don’t quite support his characterizations of them. That aside, the question arises: if the democratic public is so ignorant and biased, why is democracy (by which I mean constitutionally limited representative democracy) so successful? Of course, it might be even more successful if we implemented Brennan’s proposal and restricted voting to those who can demonstrate that they possess a basic level of knowledge. But societies that have restricted voting, past or present, don’t seem to be markedly more successful than ours – on the contrary.

The case against democracy was made a long time ago, of course, by Plato. A few outliers aside, the reply has typically been to recommend a “mixed” constitution that can mitigate the vices of the people while drawing on their virtues. Against Plato, Aristotle points out that a group of people with different experiences and skills are more likely to solve a problem than a single individual – provided, of course, that they can agree on a goal and cooperate to achieve it.

On the other hand, you could see restricted suffrage as precisely one of those means of mitigating the people’s vices that are rightly made use of by a mixed constitution. That’s what today’s liberal democracies did in the past. Most of us deplore that. Perhaps Brennan has a point if we see restricted suffrage as one tool in the mixed constitution’s toolkit – but it’s not an appealing thought.