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PRINCIPLES OF AUSTRALIAN EQUITY AND TRUSTS
estoppels change the rights of the parties, while the others change them indirectly by changing
the facts. Each form has a separate history and a distinct source in law or in equity. The various
rationales — recital, grant, convention, representation, positive promise or encouragement, fraud
and mistake, and negative promise — are different. There is no single overarching principle. 3
12.70 In a similar vein, also writing extra-judicially in 2007, Justice Brereton of the Supreme
Court of New South Wales said:
That there is no overarching doctrine of common principle is reflected in the disparate operation
of the different estoppels: some estoppels are founded on unconscionability, which is irrelevant to
others; some estoppels alter the rights of the parties, others alter only the facts; some, once raised,
are permanent, whereas others may be only temporary. 4
3. K R Handley, Estoppel by Conduct and Election, Thomson, Sweet & Maxwell, London, 2006, pp 20–21.
4. P L G Brereton, ‘Equitable Estoppel in Australia: The Court of Conscience in the Antipodes’ (2007) 81
Australian Law Journal 638, p 643.
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