Privilege - GeneralGenerally, 'privilege' occurs when a confidence over communications is respected by the courts. So for instance, it will prevent some communications from being adduced in evidence in a court or disclosed to another party in pre-trial disclosure. Whether the communication is 'privileged' depends on the circumstances in which it is made, and there are several categories of privilege depending on the different circumstances.
Historically, privilege applies if the situation in which the communication arises meets the four Wigmore criterion:
. R v Nguyen
- the communication must arise in a confidence that the identity of the informant will not be disclosed;
- the confidence must be essential to the relationship in which the communication arises;
- the relationship must be one which should be “sedulously fostered” in the public good; and
- that the public interest is served by protecting the identity of the informant outweighs the public interest in getting at the truth.
In R v Nguyen (Ont CA, 2015) the Court of Appeal stated on privilege:
 Privilege is the right of a person or class of persons to exclude certain communications from evidence or to refuse to testify about matters covered by the privilege. Privilege may relate to a class of relationships – for example, solicitor-client privilege – or may be established on a case-by-case basis. . Philip Services Corp. v. Deloitte & Touche
Once a privileged relationship is established, privilege “presumptively cloaks in confidentiality matters properly within its scope without regard to the particulars of the situation”: R. v. National Post, 2010 SCC 16 (CanLII),  1 S.C.R. 477, at para. 42.
In Philip Services Corp. v. Deloitte & Touche (Ont CA, 2015) the Court of Appeal re-stated the long-respected Wigmore test for determining privilege over information and documents, whereby such data is protected by principles of both confidentiality and evidentiary non-compellability:
 The four elements examined in analyzing a case-by-case privilege – the Wigmore criteria – are as follows:. Lizotte v. Aviva Insurance Company of Canada
1. the communication must originate in a confidence that they will not be disclosed;
2. the confidentiality must be essential to the full and satisfactory maintenance of the relation between the parties;
3. the relation must be one which in the opinion of the community ought to be sedulously fostered; and
4. the injury that would inure to the relation by the disclosure of the communications must be greater than the benefit thereby gained for the correct disposal of litigation.
In Lizotte v. Aviva Insurance Company of Canada (SCC, 2016) the court sets out that there are two types of privilege, class and case-by-case:
(1) Litigation Privilege is a Class Privilege
 There are two types of privileges in our law: class privileges and case‑by‑case privileges. A class privilege entails a presumption of non‑disclosure once the conditions for its application are met. It is “more rigid than a privilege constituted on a case‑by‑case basis”, which means that it “does not lend itself to the same extent to be tailored to fit the circumstances”: R. v. National Post, 2010 SCC 16 (CanLII),  1 S.C.R. 477, at para. 46. On the other hand, “[t]he scope of [a] case‑by‑case privilege”, as the name suggests, “will depend, as does its very existence, on a case‑by‑case analysis, and may be total or partial” (National Post, at para. 52). The four “Wigmore criteria”, the last of which is a balancing of the interests at stake, are applied:
The “Wigmore criteria” consist of four elements which may be expressed for present purposes as follows. First, the communication must originate in a confidence that the identity of the informant will not be disclosed. Second, the confidence must be essential to the relationship in which the communication arises. Third, the relationship must be one which should be “sedulously fostered” in the public good (“Sedulous[ly]” being defined . . . as “diligent[ly] . . . deliberately and consciously”). . . . Finally, if all of these requirements are met, the court must consider whether in the instant case the public interest served by protecting the identity of the informant from disclosure outweighs the public interest in getting at the truth. . . . In my opinion, litigation privilege is a class privilege. Once the conditions for its application are met, that is, once there is a document created for “the dominant purpose of litigation” (Blank, at para. 59) and the litigation in question or related litigation is pending “or may reasonably be apprehended” (para. 38), there is a “prima facie presumption of inadmissibility” in the sense intended by Lamer C.J. in R. v. Gruenke, 1991 CanLII 40 (SCC),  3 S.C.R. 263:
The fourth Wigmore criterion does most of the work. Having established the value to the public of the relationship in question, the court must weigh against its protection any countervailing public interest such as the investigation of a particular crime (or national security, or public safety or some other public good). [paras. 53 and 58]
The parties have tended to distinguish between two categories: a “blanket”, prima facie, common law, or “class” privilege on the one hand, and a “case‑by‑case” privilege on the other. The first four terms are used to refer to a privilege which was recognized at common law and one for which there is a prima facie presumption of inadmissibility (once it has been established that the relationship fits within the class) unless the party urging admission can show why the communications should not be privileged (i.e., why they should be admitted into evidence as an exception to the general rule). [Emphasis deleted; p. 286] From this perspective, litigation privilege is similar to settlement privilege and informer privilege, which the Court has already characterized as class privileges: Sable Offshore Energy Inc. v. Ameron International Corp., 2013 SCC 37 (CanLII),  2 S.C.R. 623, at para. 12; R. v. Basi, 2009 SCC 52 (CanLII),  3 S.C.R. 389, at para. 22. Like them, litigation privilege has long been recognized by the courts and has been considered to entail a presumption of immunity from disclosure once the conditions for its application have been met: Blank, at paras. 59‑60; Compagnie d’assurance AIG du Canada v. Solmax International inc., 2016 QCCA 258, at paras. 4‑8 (CanLII); Groupe Ledor inc., at paras. 8‑9; St‑Pierre, at para. 41; Axa Assurances inc. v. Pageau, 2009 QCCA 1494, at para. 2 (CanLII); Conceicao Farms Inc. v. Zeneca Corp. (2006), 2006 CanLII 31976 (ON CA), 83 O.R. (3d) 792 (C.A.), at paras. 20‑21; College of Physicians and Surgeons of British Columbia v. British Columbia (Information and Privacy Commissioner), 2002 BCCA 665 (CanLII), 23 C.P.R. (4th) 185, at paras. 31‑33 and 72; Apotex Fermentation Inc. v. Novopharm Ltd. (1994), 95 Man. R. (2d) 186 (C.A.), at paras. 18‑20; R. v. Brouillette (1992), 1992 CanLII 3599 (QC CA), 78 C.C.C. (3d) 350 (Que. C.A.), at p. 368; Opron Construction Co. v. Alberta (1989), 1989 ABCA 279 (CanLII), 100 A.R. 58 (C.A.), at para. 5.