What is a primary source?

A primary source is an original source. It has not been changed, interpreted or reworked by others.

When you use a primary source, you are citing something directly from the original. Your interpretation, analysis or paraphrase is then based on what the source actually says. This makes it easy for your teacher or examiner to verify the facts, and assess your independent thinking.

What is a secondary source?

A secondary source builds on a primary source. It is someone else's interpretation, summary or analysis of a primary source.

When you use a secondary source, you are seeing the original through someone else's eyes. This can be useful, but it can also introduce errors. A secondary source may:

Interpret the original differently than you would.
Contain mistakes or misunderstandings.
Include typos or incorrect figures.

If you rely solely on secondary sources, you risk repeating other people's errors.

When is it acceptable to use a secondary source?

Sometimes it is difficult or impossible to access the primary source. In those cases, using a secondary source is acceptable, for example when:

The primary source is hard to obtain (out of print, not held by the library).
The primary source is in a language you cannot read.
You have limited time, for example during a take-home exam, and the primary source is not available.