The Invisible Constitution in Comparative Perspective

MZXOT v. Minister for Immigration and Citizenship (2008) 233 CLR 601, 623 [39] (Gleeson 

CJ, Gummow and Hayne JJ); 629 [64] (Kirby J).

109 

J Goldsworthy, ‘Justice Windeyer on the Engineers’ Case’ (2009) 37 Federal Law Review 363 

371–2.

110 

Ibid.

111 

Victoria v. Commonwealth (the Payroll Tax Case) (1970) 122 CLR 353, 402.

112 

McGinty v. Western Australia (1996) 186 CLR 140, 168; approved in Kruger v Commonwealth 

(1997) 190 CLR 520, 567 (Gummow J).

113 

For doubts, see APLA Ltd v. Legal Services Commissioner (NSW) (2005) 224 CLR 322, 452–4 

[384]–[389] (Hayne J); Goldsworthy, chapter note, 170; J. Kirk, ‘Constitutional Implications 

(I): Nature, Legitimacy, Classification, Examples’ (2000) 24 Melbourne University Law Review 

645, 651–2, 656–7, 676.

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The Implicit and the Implied in a Written Constitution 

137

contractual.

114

 One is practical necessity (or in contract law, business efficacy): 

it consists of an alleged implication being practically necessary to enable some 

or all of the provisions of a legal instrument to be efficacious or achieve their 

intended purposes.

115

 This can be called the ‘practical necessity test’.

The other kind is decisional necessity: it consists of interpreters being com-

pelled to acknowledge an alleged implication because it is so obvious as not 

to be reasonably deniable. In contract law, the question has sometimes been 

said to be whether the court is ‘necessarily driven’ to the conclusion that some 

term is implied.

116

 Lord Esher used the term in this sense when he said: ‘nec-

essary Implication means, not natural Necessity, but so strong a Probability of 

Intention, that an Intention contrary to that, which is imputed . . . cannot be 

supposed’.

117

 The term ‘necessary’ is used loosely here: what is really required 

is not that the implication cannot possibly be denied, but that it cannot rea-

sonably be denied.

118

 Since a genuine implication depends on the author or 

speaker having a certain communicative intention, this amounts to a require-

ment that such an intention is, in the circumstances, obvious. This might be 

called the ‘obviousness test’.

119

In  Australian Capital Television v. The Commonwealth, in which the 

Australian High Court first claimed to discover in the Constitution an implied 

freedom of political communication, Mason CJ observed that implications 

may be derived from the actual terms of the Constitution if ‘the relevant 

intention is manifested according to the accepted principles of interpreta-

tion’, but that ‘structural rather than textual’ implications ‘must be logically 

or practically necessary for the preservation of the integrity of [some consti-

tutional] structure’.

120

 By ‘textual’ implications ‘manifested according to the 

accepted principles of interpretation’, which do not need to be ‘necessary’, he  

114 

Discussed in Goldsworthy, chapter note, 168–70. See also E. Peden, Good Faith in the Inter-

pretation of Contracts (2003) 60–71.

115 

The version found in contract law is called the ‘business efficacy’ test: see Starke, Seddon and 

Ellinghaus, Cheshire & Fifoot’s Law of Contract (6th Aust’n edn 1992) 212–13. As for statutes, 

see Slipper Island Resort Ltd v. Minister of Works & Development [1981] 1 NZLR 136, 139.

116