What is the difference between privilege and discovery?

The tension between privilege and discovery is a manifestation of two competing policies. The purpose of discovery is to advance the search for the truth of the dispute between the parties. The purpose of the privilege, which may result in the suppression of the truth, is to protect the legal system. There is a public interest in persons being able to confide freely and frankly in their legal advisers for the purpose of obtaining skilled, professional legal advice without fear that their confidences will be disclosed to third parties and used against them: Smith v. Jones, 1999 CanLII 674 (SCC), [1999] 1 S.C.R. 455 at paras. 45-47.

The rule was historically considered to be an evidential one but it is now recognized that it is part of a broader substantive right of confidentiality and is "a principle of fundamental importance to the administration of justice": Smith v. Jones, supra, at paras. 48-50.

The privilege is not absolute, however, and it has long been recognized that communications that are obtained to facilitate the commission of a crime or a fraud are not protected: see Solosky v. The Queen (1979), 1979 CanLII 9 (SCC), [1980] 1 S.C.R. 821, per Dickson J. (as he then was) at p. 835.