What is an affidavit and when is it used in Ontario civil litigation?

An affidavit is a written, sworn statement of facts made under oath or affirmation before a commissioner for taking oaths, a notary public, or another authorized official. In Ontario civil litigation, affidavits are used extensively in motions (as the primary form of evidence for interlocutory hearings), in summary judgment proceedings, in support of applications, and in various procedural steps such as the Affidavit of Documents.

An affidavit must contain only facts within the deponent's (the person swearing the affidavit's) personal knowledge, except where the affidavit is expressly permitted to include belief statements and the source of that belief is disclosed. Opinions are generally not appropriate in a lay person's affidavit. The affidavit should be organized clearly, use plain language, and attach any relevant documents as exhibits.

Making a false statement in an affidavit is perjury, a serious criminal offence. Courts scrutinize affidavit evidence carefully, and inconsistencies between an affidavit and other evidence can significantly damage the deponent's credibility. Before finalizing an affidavit, review it carefully with your lawyer to ensure it is accurate, complete, and consistent with your other evidence. The opposing party has the right to cross-examine the affiant on the contents of the affidavit, so what you swear to must be something you can defend under questioning.