The scope for courts to imply words into a statute has expanded over time. In 1910, Lord Mersey said: "it is a strong thing to read into an Act of Parliament words which are not there, and in the absence of clear necessity it is a wrong thing to do" . These days, it is accepted that courts "may read words into a legislative provision if by inadvertence Parliament has failed to deal with an eventuality required to be dealt with if the purpose of the Act is to be achieved".
However, the circumstances in which courts will be prepared to read words into legislation depend, like most questions of statutory interpretation, on the legislative context.
The Victorian Supreme Court recently considered this issue in XX v WW and Middle South Area Mental Health Service  VSC 564.
The involuntary treatment order
The issue arose in the context of an appeal against an involuntary treatment order (ITO) made under the Mental Health Act 1986 (Vic).
The plaintiff had been detained and treated against her will under an ITO. The Mental Health Review Board, which has a supervisory role in relation to such orders, made an order discharging the ITO. Later on the same day, the defendant, a registered medical practitioner (RMP), recommended that a further ITO be made.
The plaintiff argued that the RMP had acted unlawfully in making that recommendation.
The statutory background: the Mental Health Act 1986 (Vic)
Section 8(1) of the Act set out mandatory criteria for involuntary treatment: the person must appear to be mentally ill, the mental illness must require immediate treatment, involuntary treatment must be necessary for the health or safety of the person or protection of the public and the person must have refused, or be unable to, consent to the treatment and not able to receive adequate treatment in a less restrictive manner.
Section 9(1) of the Act required that a request for involuntary treatment be accompanied by a recommendation by a RMP following a personal examination of the person.
At issue was the interpretation of section 9(3), which provided that a RMP "must not make a recommendation under subsection (1) unless he or she considers that (a) the criteria in section 8(1) apply to the person, and (b) an involuntary treatment order should be made".
The plaintiff's argument: a further limitation should be read into the Act
The plaintiff argued that a further limitation should be implied into section 9(3) to deal with the situation where an RMP is aware that the Board has recently ordered the discharge of an ITO against the person. In those circumstances, the plaintiff contended, section 9(3) should be read as if it contained an additional limitation, namely that the RMP must not recommend the making of a further ITO without having formed a reasonable and good faith opinion, on the basis of information not known to the Board, which put a significantly different complexion on the case.
Underlying this argument was a contention that, given the Board's supervisory role, its decisions must be respected by RMPs. It would be inconsistent with the power of the Board to hear appeals against ITOs, so the argument went, if its decision to discharge such an order could be disregarded by a RMP in the absence of changed circumstances and for no other reason than that the practitioner disagreed with the Board's decision.
Should the limitation be implied?
Justice McDonald found "considerable force" in that contention.
He also accepted that a purposive construction of a legislative provision allows the adding of words that expand the provision's field of operation, provided that four conditions are met:
- The court knows the mischief with which the Act was dealing.
- The court is satisfied that by inadvertence Parliament has overlooked an eventuality which must be dealt with if the purpose of the Act is to be achieved.
- The court is able to state with certainty what words Parliament would have used to overcome the omission if its attention had been drawn to the defect.
- The modified construction is reasonably open, not unnatural, incongruous or unreasonable, and consistent with the statutory scheme. 
However, after considering section 9(3) in the context of the Act as a whole, Justice McDonald declined to imply the limitation for which the plaintiff contended. The Act contained significant checks and balances, including procedural steps that an RMP must follow before making an ITO, and a requirement for review of the patient by an authorised psychiatrist. Such requirements, Justice McDonald said, "weigh heavily against a finding that Parliament overlooked the potential for an ITO to be recommended in circumstances where a Board had discharged a pre-existing ITO". Moreover, the combined effect of such requirements means that an RMP in this situation must have regard to decisions of the Board to discharge an ITO and its reason for doing so.
Justice McDonald commented that a recommendation for a new ITO in these circumstances would be lawful only if the RMO "has acted in good faith, has not acted arbitrarily or capriciously or taken into consideration matters which are excluded by statute expressly or by necessary implication".
The effect of the Charter of Human Rights and Responsibilities Act 2006
The plaintiff also argued that her contended limitation was required by section 32(1) of the Charter of Human Rights and Responsibilities Act 2006.
Justice McDonald rejected that argument, noting that "section 32(1) does not allow the reading in of words which are not explicit in a provision, or the reading down of words so far as to change the true meaning of a provision. Nor does it authorise a process of interpretation which departs from established understanding of the process of construction".
XX v YY is a timely reminder for decision-makers, and for those seeking to challenge statutory decisions, that while courts can imply words of limitation, they are likely to be reluctant to do so, even where the decision impacts significantly on individual rights. In such cases, courts will look to the purpose and context of the legislation as a whole, and to principles of administrative law, to supply the appropriate safeguards.
 Thompson v Gould & Co  AC 409 at 420 per Lord Mersey Back to article
 Bermingham v Corrective Services Commission of New South Wales (1988) 15 NSWLR 292 Back to article
 at -; see Bermingham v Corrective Services Commission of New South Wales (1988) 15 NSWLR 292 per McHugh J at 302; Director of Public Prosecutions v Leys (2012) 296 ALR 96 (Redlich and Tate JJA and Forrest AJA) Back to article