Both expressions refer to a declaration received by a person legally authorized to do so — a Commissioner for Oaths, notably — during which the declarant confirms the truthfulness of what they are stating. The difference lies in the wording used for that confirmation.
What is a declaration under oath?
In a declaration under oath, the declarant swears that what they are stating is true, using wording that may invoke their personal or religious beliefs. The commissioner receives that oath and attests that the formality was properly observed.
What is a solemn declaration (or solemn affirmation)?
A solemn declaration — also called a solemn affirmation — lets a person solemnly affirm the truthfulness of their statement instead of swearing an oath, using wording that makes no reference to a deity. A person may choose this form for reasons of personal belief, among others.
Does it change anything for you?
In the vast majority of cases, no. Both forms are received by the same commissioner, follow a similar procedure, and produce the same effect once duly received. What matters most is that the form chosen matches the declarant's beliefs and that the applicable procedure was followed.
Why does this distinction exist?
This distinction lets anyone make a solemn declaration before an authorized person, regardless of their religious or personal beliefs — without being required to swear an oath that invokes a deity if that does not match their beliefs.
Does an official form always specify which one to use?
Some official forms already carry a specific title — for example, "statutory declaration" for several federal immigration forms. Even then, the declarant generally keeps the right to choose the form that matches their beliefs; the commissioner adapts the wording accordingly.
Can this declaration be made online?
Yes. In Québec, a Commissioner for Oaths can receive a declaration under oath or a solemn declaration remotely, by videoconference, when the applicable conditions are met.
Online oath commissioning in Québec: how does it work?
Assermentation Express
Assermentation Express is not a government website. This service does not determine which of the two forms applies to your situation, nor the requirements specific to your document — the commissioner will guide you on the appropriate wording at the time of the session.