In Western Australia, actual knowledge (not constructive knowledge) of the other party's mental incapacity is required to render a contract voidable, following Giles v Rooney and the High Court's observations in Gibbons v Wright. An administration order under s 64 of the Guardianship and Administration Act 1990 (WA) does not conclusively establish that the person lacked common law contractual capacity at an earlier date, because the statutory test differs from the common law test. The inquiry into contractual capacity is issue-specific and must be assessed by reference to the particular transaction, taking into account whether the person could understand the general nature of the transaction when it was explained to them.
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