Sometimes the best way to describe people is to describe the effect they have on us. This can be said of Anders Behring Breivik, who has aroused feelings of anger, coldness, darkness, and emptiness in onlookers around the world. Nearly everything about him can be described in these terms; the way he confessed to killing 77 people in Oslo and on Utoya Island on July 22 2011, his testimony in court, even his appearance.

Currently Norway’s legal system is struggling to come to terms with Breivik and in particular to discover whether in fact he is insane. If so, he will spend possibly the rest of his life in a mental institution. If not, he will spend at least 21 years, but possibly the rest of his life in jail.

In fact it is no easy task the courts face. Prosecutors, the public, and Breivik himself are fairly set on his sanity, and his defence lawyers don’t seem really sure. Two court-ordered psychiatric review found him insane and sane respectively.

Commenting on the case, one Norwegian lawyer noted, “Experience, however, has shown it is difficult to predict what psychiatrists will conclude – often it is the opposite of what one might think.” Norwegians are masters of understatement.

The imprecision of psychiatry is a part of the problem. There are no tests for insanity. Another part is the fact that insanity itself is a legal term, not a current medical one. Insanity in the English-speaking world is usually associated with a lack of insight into the moral content of an action. In Norway, the definition is broader. A psychotic state of mind can justify an insanity plea.

Put most simply, a psychotic state of mind is one in which a person is disconnected from reality. In the initial psychiatric report, Breivik was diagnosed with paranoid schizophrenia. The report said he lived in a delusional universe, seeing himself as “Europe’s most perfect knight since WWII”, called upon to launch a counter-attack on the Islamicization of Europe. It also described a man with a blunted emotional response and a severe lack of empathy.

A second report released just this month took a different view. Breivik had a narcissitic personality disorder, but he was not psychotic. The preparation and execution of the killings seemed to be too well thought out for that.

The medical question will be difficult to resolve. But insanity is not purely a medical question, it is also a commonsense question. Breivik is pretty clearly insane in a “commonsense” sense. His action was clearly not committed in a fit of passion — it was coldly planned and cruelly executed. Nor are there any real grounds for saying he did not have the use of reason. Much of his testimony is chillingly reasonable within the sphere of his worldview.

So what is his worldview? Taking out the confusion of political and racial content (which occupies a good part of his 1,500 page manifesto 2083 – A European Declaration of Independence) it boils down to a belief in the will to power, and in his personal right to wield it. It is the insanity of a person whose reason and will are in working order but are beholden to no one. It is the insanity of a person who creates his own world, and alone understands it. In Chesterton’s words: “The madman is not the man who has lost his reason. The madman is the man who has lost everything except his reason.”

Breivik’s insanity is the kind that says: “If I really think about something, agonise over something, and really believe in myself, I must be right.” In that sense he shares his madness, to a lesser degree, with many.

Is this insanity criminal? Certainly it is disconnected from the world. As a support group leader involved in the case said: “He’s not in our world. He isn’t, and he doesn’t have humanity at all. The way I slap little mosquitoes in the summer, that’s how he is about human lives.”

But psychiatrists don’t say why this disconnection occurs. As it currently stands, psychiatry lacks the narrative to do that. The rupture with reality in Breivik’s case doesn’t seem to be purely the result of a known mental illness. There would seem to be something in that sense of anger, coldness, darkness and emptiness that points to what common sense would call evil. That’s what makes his case so especially confronting.

We might still take the approach of one Norwegian schoolgirl: “It doesn’t matter whether he is locked up in a psychiatric institution or in a prison, as long as he is locked up.” There is a rare degree of sense in that, and in terms of threat to society she is right.

But I would suggest a few reasons why Breivik should go to prison. Firstly, given the nature of his “insanity”, it seems very unlikely that extended psychiatric treatment would really change him. Secondly, no matter how good a justice system is at rehabilitating and reforming people, if it does not give the families of victims and society as a whole a sense of justice, it is betraying its purpose.

Finally, and crucially, it would be a worthwhile thing for Norway and the world to call an action like this evil. One would hope we still have the spiritual resources for that. Breivik has said he wants to be taken seriously, he does not want to be considered insane. We may think, therefore, that calling his action insane would be a good way to counter his rhetoric. But  insanity, in his own words, “provides new opportunities”.

Whatever Breivik may have said about good and evil, he clearly doesn’t believe in them. He described the killings as “a small barbarian act to prevent a larger barbarian act.” They were justified in his own mind, and so they were right. Only a concept of good and evil that goes beyond the individual and beyond society can cure this madness.

Phillip Elias is a Sydney doctor.