One of the most famous photographs of the Battle of Vimy Ridge shows men of Vancouver's 29th Battalion walking across no man's land, with fallen soldiers in the foreground and shells bursting behind them. It was made by William Ivor Castle, an official photographer for the Canadian War Records Office, which recorded the war and promoted Canada's war effort, and it was exhibited in London in July 1917. Historians later showed that it is a composite: Castle built it from at least three negatives, adding the fallen soldiers in the foreground to make the scene more dramatic. The soldiers were real, the battle was real, and the photograph is still valuable evidence, but of what the war effort wanted the public to see, not simply of what the attack looked like. Today, with AI tools that can invent a "historical photo" in seconds, asking who made a source, why, and how is more important than ever.
Primary and secondary sources
A primary source was created at the time being studied, or by someone who took part in or witnessed the events: a soldier's letter, a diary, a photograph, a newspaper from the time, a law, census data, a treaty, a political cartoon, an artifact, or an oral history told by someone who lived it or who carries a community's history. A secondary source interprets the past from a later vantage point, usually by putting many primary sources together: a history book written later, a documentary, an encyclopedia article or a museum website. Whether a source is primary or secondary depends on your question. A 1967 magazine article about the First World War is a secondary source about the war, but a primary source if you are asking how Canadians in the 1960s remembered the war.
| Source | Primary or secondary? | What it can show | What to watch for |
|---|---|---|---|
| A soldier's letter home from France, 1917 | Primary | Personal experience, feelings, daily life at the front | Wartime censors read letters; soldiers often hid the worst from family |
| A Montreal French-language newspaper, 1917 | Primary | Opinions and arguments circulating in Quebec at the time | Each paper had an editorial position and a target readership |
| The Military Service Act, 1917 | Primary | Exactly what the law required | A law shows intentions, not how it was enforced or received |
| Census data from 1931 | Primary | Population, jobs, origins and language patterns | Categories reflect the assumptions of the people who designed the census |
| A survivor's testimony to the Truth and Reconciliation Commission | Primary | Lived experience of residential schools in the survivor's own words | Shared with consent and under protocols; treat with respect |
| A history book written later about the Depression | Secondary | An expert's interpretation built from many sources | Check the author's evidence, date and argument |
| A documentary about the October Crisis | Secondary | A visual, narrated interpretation, often with interviews | Editing choices shape the story; interviews inside it are primary |
Oral histories and oral traditional knowledge
Many First Nations, Métis and Inuit communities have recorded their histories, laws and connections to the land for many generations through oral tradition: carefully kept accounts, songs, ceremonies and teachings passed on by Elders and Knowledge Keepers, often with rules about who may tell them and when. Canadian courts once gave such evidence little weight. In the Delgamuukw case, the Gitxsan and Wet'suwet'en peoples presented their oral histories, including the Gitxsan adaawk and the Wet'suwet'en kungax, to support their title to their territories in northern British Columbia. The trial judge dismissed much of this evidence in 1991, but on December 11, 1997, the Supreme Court of Canada ruled that the laws of evidence must be adapted so that oral histories are placed on an equal footing with the written documents courts usually rely on. Oral histories are also central to more recent Canadian history: the Truth and Reconciliation Commission heard from about 6,500 Survivors and other witnesses, and veterans' interviews preserve memories of both world wars.
- Ask permission and follow protocol: some knowledge is shared only in certain settings or by certain people; a community or Knowledge Keeper decides what can be recorded and shared.
- Name the source accurately: the person's name (if they agree), their role, their Nation or community, and the date.
- Do not treat oral history as "less reliable" by default: judge it like any source, by who holds it, how it has been kept and passed on, and how it connects with other evidence.
- Corroborate respectfully: oral histories, documents, archaeology and maps can support one another; where they differ, ask why rather than assuming the written record wins.
Assessing credibility
- Author: who made it? What was their position, expertise and connection to the events?
- Date and context: when was it made, and what was happening then? Was it made during the events or long after?
- Purpose: why was it made: to inform, persuade, entertain, record privately, or sell?
- Audience: who was it for? A private diary, a government report and a recruiting poster speak to different people.
- Bias and perspective: whose point of view does it show, and whose is missing? Is it one-sided on purpose?
- Corroboration: do other independent sources confirm it? One source alone is weak evidence for a big claim.
- Usefulness: even a biased source is useful evidence of what its creator believed or wanted others to believe.
- Author: the campaign of Prime Minister Borden's pro-conscription Union Government.
- Purpose: to win votes in the December 1917 election by urging support for conscription and for the soldiers overseas.
- Audience: mainly English-speaking voters, including the soldiers' female relatives newly able to vote.
- Techniques: emotional images and appeals to loyalty, duty and not abandoning the troops.
- Useful as evidence of: the arguments the government and its supporters used, and the emotions they tried to stir.
- Author: Henri Bourassa, founder and editor of the Montreal newspaper Le Devoir and a leading French-Canadian nationalist.
- Purpose: to persuade readers that conscription was unjust and that Canada had already given enough to a British imperial war.
- Audience: French-speaking readers, especially in Quebec.
- Techniques: reasoned argument and appeals to Canadian rather than British imperial interests; Bourassa had also campaigned against Ontario's Regulation 17.
- Useful as evidence of: the main arguments of the anti-conscription movement, though one paper does not speak for all of Quebec.
Manipulated and AI-generated images
Images have been staged, retouched and combined since the early days of photography, as Castle's Vimy composite shows. Today's AI image generators make it easy to produce convincing fakes, including fake "archival" photos of historical events, and they spread quickly on social media. Before you use an image as evidence, trace it to its origin: a reliable archive such as Library and Archives Canada or a museum should give the creator, date and an item number. Try a reverse image search to see where it first appeared. Look for warning signs such as garbled text on signs and uniforms, extra or blurred fingers, objects that did not exist at the time, or lighting that does not match. Check whether the image was colourized or cropped, which changes how it looks without changing the event. Finally, corroborate: if a dramatic photo of a famous event appears nowhere in archives or reputable histories, treat it as suspect.
Citing your sources
| Source type | Chicago footnote (first time you cite it) | Chicago bibliography entry |
|---|---|---|
| Book | 1. Tim Cook, Shock Troops: Canadians Fighting the Great War, 1917–1918 (Toronto: Viking Canada, 2008), [page number]. | Cook, Tim. Shock Troops: Canadians Fighting the Great War, 1917–1918. Toronto: Viking Canada, 2008. |
| Website article | 2. Gérald A. Beaudoin, "Delgamuukw Case," The Canadian Encyclopedia, last modified January 11, 2019, https://www.thecanadianencyclopedia.ca/en/article/delgamuukw-case. | Beaudoin, Gérald A. "Delgamuukw Case." The Canadian Encyclopedia. Last modified January 11, 2019. https://www.thecanadianencyclopedia.ca/en/article/delgamuukw-case. |
| Archival photograph | 3. Canada, Department of National Defence, Canadian machine gunners in shell holes on Vimy Ridge, April 1917, photograph, [item number from the archive record], Library and Archives Canada, Ottawa. | Canada. Department of National Defence. Canadian machine gunners in shell holes on Vimy Ridge. April 1917. Photograph. [Item number from the archive record]. Library and Archives Canada, Ottawa. |
| Oral history interview | 4. [Name, role, Nation or community], interview by [your name], [place], [date], shared with permission. | Usually cited in the notes only; follow any wishes the speaker or community has expressed about how they are named. |