Courts - Amicus Curiae. R. v. Kahsai
In R. v. Kahsai (SCC, 2023) the Supreme Court of Canada considered generally the role of amicus curiae, here in a criminal appeal. The court unfortunately makes no distinction between civil and criminal amicus (the case overwhelmingly focusses on criminal), but readers may find some aspects of it useful for civil cases as well:
 The power to appoint amicus curiae flows from the inherent jurisdiction of superior courts to manage their own procedure to ensure a fair trial (CLAO, at para. 46; I. H. Jacob, “The Inherent Jurisdiction of the Court” (1970), 23 Curr. Legal Probs. 23, at pp. 27-28). This jurisdiction empowers a superior court judge to appoint amicus when the judge believes doing so is required for the just adjudication of a case. The power of a statutory court to appoint amicus is necessarily implied from the court’s authority to control its own process and function as a court of law (CLAO, at paras. 12 and 112). The discretionary power to appoint amicus should be used “sparingly and with caution, in response to specific and exceptional circumstances” that arise (para. 47).
 Although not a party to the proceedings, an amicus may help the court by providing a perspective or performing a function that the judge considers necessary to decide the issues in dispute (CLAO, at paras. 44 and 87). This role is justified on the reasoning that a court should not have to decide “contested, uncertain, complex and important points of law or of fact without the benefit of thorough submissions”, which may not be available from the parties acting alone (para. 108). The defining feature of amicus is that they owe their duty of loyalty exclusively to the court, regardless of the circumstances or the specific terms of their appointment (paras. 53, 87 and 118). While the purpose of an amicus appointment must be to assist the court, it may have the incidental effect of advancing the interests of the accused (see M. Vauclair and T. Desjardins, in collaboration with P. Lachance, Traité général de preuve et de procédure pénales 2022 (29th ed. 2022), at para. 26.6, citing CLAO, at para. 119).
 The role of amicus is highly adaptable and can encompass duties that exist on a broad spectrum of functions (see R. v. Walker, 2019 ONCA 765, 381 C.C.C. (3d) 259, at para. 65; CLAO, at para. 117). The precise role for amicus will depend on the particular needs identified by the trial judge. But the role of amicus is not without limits. ...