As well as defining sources as popular and scholarly, information sources can be defined as being primary, secondary or tertiary - first-hand, second-hand or third-hand. This classification are based on how close the source is to where the information comes from. This lets you know whether the author is reporting original information or is writing about the work of others.
Primary sources are immediate, first-hand accounts of a topic, from people directly involved. Primary sources provide information in its original or purest form, without it having been changed in any way. Examples of primary sources include:
Secondary sources are one step removed. Secondary sources provide information about primary sources. These sources review, analyse or interpret the original primary source information. They can provide more in-depth analysis of the content but might introduce bias.
Secondary sources are often created by experts in that topic. Examples of secondary sources include
Tertiary sources bring together and organise primary and secondary source material.
Primary Sources regarding popular singer Billie Eilish might include:
Secondary sources might include:
Tertiary sources might include:
For first-hand information that should be free from second-hand comment, use primary sources. However primary sources lack perspective. Secondary sources are good for providing context and analysis, while tertiary sources are good for finding authoritative and reliable primary and secondary sources.
Declaration of war against Bulgaria: The London Gazette, 19th October 1915, available available under the Open Government Licence v3.0
Linguistics textbooks by Wikipedia user "Hoary" licenced under the Creative Commons Attribution-Share Alike 4.0 International licence
Encyclopaedia Britannica adapted from Wikipedia user "Ziko" licensed under the Creative Commons Attribution-Share Alike 3.0 Unported, 2.5 Generic, 2.0 Generic and 1.0 Generic license
Billie Eilish: Attribution: © Glenn Francis, www.PacificProDigital.com. (Toglenn, CC BY-SA 4.0, via Wikimedia Commons)