John Roughan is a good political commentator, but he is not right about section 59 of the Crimes Act 1961. The law it lays down is far from clear.

Since much confusion exists about the section, let me try to clarify its effect as briefly as possible.

Section 59 is among those sections of the Crimes Act 1961 that establish defences to crimes. Like other sections of this type, it can apply to a number of different offences, both in that act and in others.

However, the offences most likely to be involved in a case to which it is relevant are common assault (s196 of the Crimes Act 1961), which carries a maximum punishment of imprisonment for one year, and assault on a child (s194), which carries a maximum punishment of imprisonment for up to two years.

The new section 59, introduced in 2007, replaced the previous section, which allowed a parent (or person in the place of a parent) to use reasonable force by way of correction towards a child, with a more limited defence.

As Roughan pointed out, subsection (1) of the new section 59 allows a parent (or person in the place of a parent) to use force that is reasonable in the circumstances for the purpose of (a) preventing or minimising harm to the child or another person, (b) preventing the child from engaging in a criminal offence, (c) preventing the child from engaging in offensive or disruptive behaviour, or (d) performing the normal daily tasks incidental to good care and parenting.

Roughan considers this allows a light smack in the supermarket to stop stealing or a light smack to stop a child running in front of a car, and so on. He may be right, although that is not clear. Possibly the only force that can be used is to restrain the child physically.

The problem is the section doesn't stop with subsection (1). Subsection (2) says: "Nothing in subsection (1) justifies the use of force for the purpose of correction." Then, for good measure, subsection (3) says: "Subsection (2) prevails over subsection (1)."

Subsection (4) then adds that the police have a discretion not to prosecute complaints against a parent, when the offence is so inconsequential that there is no public interest in prosecuting.

This section is a mess. Subsection (2) seems to take away much of what is allowed by subsection (1). Just how one makes overall sense of it is not clear. The sop in subsection (4) does not help: it makes it more likely that its application will be arbitrary. Parents, don't get on the wrong side of officials!

Roughan thinks that subsection (2) will be limited to correction that is different to the sort of smack he thinks is allowed by subsection (1). He suggests it will be limited to smacking that takes place too late to stop or prevent the relevant behaviour. That, he says, tends to be a different sort of beast.

Well, certainly, subsection (2) will preclude smacking that is too late to stop or prevent the relevant bit of behaviour, but it is not clear this is all it will preclude. What causes difficulty is that often the same act of smacking will be motivated by both a preventative and a corrective purpose.

Consider the following scene. Mother (seeing Johnny take a packet of sweets off the confectionery stand, as she waits in the supermarket queue): "Johnny, I have told you many times you can't do that. It is stealing." (She puts the sweets back.) Mother (after Johnny has taken the sweets again, when her attention was diverted): "Johnny, I have told you not to do that." (She puts the sweets back again.) Run this line as many times as you think mother's patience will stand. Mother (after Johnny has taken the sweets once more): "All right Johnny, I have warned you and warned you." (She smacks his hand.)

Here, there are plainly two purposes involved: a preventative purpose (to stop the thieving) and a corrective purpose (to prevent Johnny doing it again in the future). Which subsection prevails in this situation?

On a strict reading, subsection (2) does: for it says nothing in subsection (1) justifies the use of force for the purpose of correction. And Mother, we have to allow, did use force for the purpose of correction, even if that was not her only purpose.

It is possible that the courts might apply a dominant purpose approach to section 59, as they sometimes do in other similar situations involving mixed purposes. They might say that Parliament must have intended that the defence ceases to apply only when correction was the dominant purpose. That would mean that if prevention was the dominant purpose a defence would still be available.

I don't think that can be guaranteed. Further, even if this approach is taken, it is often going to be very difficult sorting out which was the dominant purpose. Mother had better hire a good lawyer.

This is not clear legislation. In creating this law, Parliament abandoned its constitutional responsibility to say with clarity just which conduct is criminal.

The section results from a political fudge. Whatever other views one takes about the topic of smacking, that much at least ought to be kept clear.

* Jim Evans is emeritus professor of law at Auckland University.