6.3 Relevant principles
45 The question of whether or not a statutory decision maker has exercised its power reasonably is fact sensitive and will depend on the whole of the circumstances prevailing at the time of the decision: Singh at [48] (Allsop CJ, Robertson and Mortimer JJ).
46 It is now clear that jurisdictional error may lie in circumstances where the discretion of the Tribunal in failing to allow an adjournment has miscarried: Li at [47] (Hayne, Kiefel and Bell JJ). Because s 363(1)(b) contains a statutory discretionary power, the standard to be applied to the exercise of that power is that it will be exercised reasonably: Li at [63]. The standard of reasonableness is to be ascertained having regard to the scope and the purpose of the statute conferring the discretionary power: Li at [67]; see also Project Blue Sky Inc v Australian Broadcasting Authority [1998] HCA 28; 194 CLR 355.
47 In BJK17 v Minister for Immigration, Citizenship, Migrant Services and Multicultural Affairs [2019] FCAFC 171; 272 FCR 15 the Full Court said at [41] (Middleton, Bromberg and Snaden JJ):
…There are no fixed categories of circumstances by reference to which a failure to exercise, or consider exercising, the discretion might be impugned as legally unreasonable: CCQ17 v Minister for Immigration and Border Protection [2018] FCA 1641 at [42] (Thawley J). Rather, an assessment of whether, in any given case, the exercise or non-exercise of the discretion is attended by legal unreasonableness must, of necessity, be case-specific: Minister for Immigration and Border Protection v Singh (2014) 231 FCR 437 at [42] (Allsop CJ, Robertson and Mortimer JJ). A decision will not be impugned as legally unreasonable simply because it is one about which different minds might form different views: Plaintiff S111/2017 v Minister for Immigration and Border Protection (2018) 263 FCR 310 at [66] (Perry J, with whom McKerracher and Charlesworth JJ agreed).
48 Unreasonableness is not, however, a basis for the court to set aside a decision with which it simply disagrees. As French CJ said in Li at [30]:
The requirement of reasonableness is not a vehicle for challenging a decision on the basis that the decision-maker has given insufficient or excessive consideration to some matters or has made an evaluative judgment with which a court disagrees even though that judgment is rationally open to the decision-maker. Gleeson CJ and McHugh J made the point in Eshetu that the characterisation of somebody's reasoning as illogical or unreasonable, as an emphatic way of expressing disagreement with it, "may have no particular legal consequence." As Professor Galligan wrote:
"The general point is that the canons of rational action constitute constraints on discretionary decisions, but they are in the nature of threshold constraints above which there remains room for official judgment and choice both as to substantive and procedural matters. In other words, within the bounds of such constraints, different modes of decision-making may be employed."
(citations omitted)
49 In that same case, the majority (Hayne, Kiefel and Bell JJ) noted about the application of the legal standard of unreasonableness that:
[75] In Peko-Wallsend, Mason J, having observed that there was considerable diversity in the application by the courts of the test of manifest unreasonableness, suggested that "guidance may be found in the close analogy between judicial review of administrative action and appellate review of a judicial discretion". House v The King holds that it is not enough that an appellate court would have taken a different course. What must be evident is that some error has been made in exercising the discretion, such as where a judge acts on a wrong principle or takes irrelevant matters into consideration. The analogy with the approach taken in an administrative law context is apparent.
[76] As to the inferences that may be drawn by an appellate court, it was said in House v The King that an appellate court may infer that in some way there has been a failure properly to exercise the discretion "if upon the facts [the result] is unreasonable or plainly unjust". The same reasoning might apply to the review of the exercise of a statutory discretion, where unreasonableness is an inference drawn from the facts and from the matters falling for consideration in the exercise of the statutory power. Even where some reasons have been provided, as is the case here, it may nevertheless not be possible for a court to comprehend how the decision was arrived at. Unreasonableness is a conclusion which may be applied to a decision which lacks an evident and intelligible justification.
(citations omitted)
50 Ordinarily, it is necessary to prove the element of materiality in order to establish that a breach of an express or implied condition of a conferral of statutory decision-making authority resulted in jurisdictional error: MZAPC v Minister for Immigration and Border Protection [2021] HCA 17 at [1] (Kiefel CJ, Gageler, Keane and Gleeson JJ); see also Hossain v Minister for Immigration and Border Protection [2018] HCA 34; 264 CLR 123. A breach of a condition of a decision-making power will be material if there is a realistic possibility that the decision in fact made could have been different had the breach of the condition not occurred: MZAPC at [2] and [39]; see also Minister for Immigration and Border Protection v SZMTA [2019] HCA 3; 264 CLR 421. The party who bears the onus of proving jurisdictional error bears the onus of proving that the breach was material: MZAPC at [2] and [39].
51 In relation to the question of materiality in the context of legal unreasonableness, see BDJ18 v Minister for Immigration, Citizenship, Migrant Services and Multicultural Affairs [2021] FCA 1074 at [44]-[45] (Thawley J).
52 Whether it is legally unreasonable for a decision maker to not exercise a discretion is to be considered in the context of the relevant statutory scheme. That is conveniently addressed by Mortimer J in Kaur at [80]:
The Tribunal's statutory task, as revealed by a consideration of the Act as a whole and Parts 5 and 6 in particular, is to arrive at the correct or preferable decision in the case before it according to the material before it: Li 249 CLR 332; [2013] HCA 18 at [10] per French CJ, referring to Bushell v Repatriation Commission (1992) 175 CLR 408 at 425 per Brennan J. The fact that it is a tribunal dealing with particular subject matter does not alter the nature of its task, which remains the same as those tribunals on which fundamental aspects of its scheme was modelled, such as the Administrative Appeals Tribunal. The range of powers, discretions and obligations reposed in the Tribunal by Div 5 of Part 5 of the Act, and the way in which the statute conditions them, might on a first reading suggest that the Tribunal has a limited amount of decisional freedom as to how it conducts its review once it has embarked upon it. That would be an incorrect impression. Division 5 is an exhaustive statement of the rules of natural justice only insofar as the "matters" with which it deals: see Saeed v Minister for Immigration and Citizenship (2010) 241 CLR 252; [2010] HCA 23 at [37]-[39] per French CJ, Gummow, Hayne, Crennan and Kiefel JJ; Li 249 CLR 332; [2013] HCA 18 at [18] per French CJ. Outside those matters, common law procedural fairness principles apply. Those principles, read with facultative provisions such as ss 353 and 357A(3) and general powers in (for example) s 363, combine to confer on the Tribunal the necessary degrees of flexibility to ensure it can fully perform its statutory task. For example, its power of adjournment (s 363(1)(b)), the power to take evidence by telephone (s 366), the power to require the Secretary to make further investigations (s 363(1)(d)) and the power to seek information (s 359) are all illustrations of the flexibility given by the statutory scheme to the Tribunal to enable it to perform its task.
53 Of particular relevance in the present case is the relationship between the power to adjourn in s 363(1)(b) and the power in s 360(1). In Li the majority observed that the purpose of s 360(1) is to provide an applicant for review the opportunity to present evidence and arguments "relating to the issues arising in relation to the decision under review": at [60], [83].