What is the patent unreasonableness standard?

Traditionally, patent unreasonableness was seen as a defect that was so flawed that no amount of curial deference could justify letting it stand. This was referred to in Dunsmuir. . . . Iacobucci J., writing for the Court in Law Society of New Brunswick v. Ryan, [2003] 1 S.C.R. 247, 2003 SCC 20, attempted to bring some clarity to the issue. He explained the different operations of the two deferential standards as follows, at paras. 52-53: [A] patently unreasonable defect, once identified, can be explained simply and easily, leaving no real possibility of doubting that the decision is defective. A patently unreasonable decision has been described as “clearly irrational” or “evidently not in accordance with reason” … A decision that is patently unreasonable is so flawed that no amount of curial deference can justify letting it stand.