You should reference other people's work if you quote, paraphrase, or summarize the thoughts and/or ideas presented there (see previous pages). However, you do not need to reference the source when the information can be characterized as general knowledge. This is knowledge that all adults are expected to possess. Examples of general knowledge include:

Joe Biden was elected as president of the United States in 2021.
Norway is not a member of the European Union.
Gravity causes humans to not be weightless on Earth.

There is often a fluid transition between general knowledge and specific knowledge, which must be supported by sources. Have a look at this statement:

Students' mental health has worsened due to social distancing in connection with the Covid-19 pandemic

A statement like this can be considered general knowledge, as it is quite obvious that people can become more lonely when social contact becomes difficult.

However, this statement is not general knowledge because it concerns concrete data that you need to cite:

"The influenza epidemic increased slightly after a sharp decline from the peak in week 52 but fell somewhat again in weeks 7 and 8".

(Source: Norwegian Institute of Public Health (2023, March 2). Weekly reports for COVID-19, influenza and other respiratory tract infections. https://www.fhi.no/en/publ/2020/weekly-reports-for-coronavirus-og-covid-19/).

If you are unsure if something is general knowledge, you should refer to the source you find. It is always better to refer one time too many than one time too little.

Discipline-specific general knowledge

In all fields of study, there is some knowledge that can be called "discipline-specific general knowledge". This is basic knowledge within the field of study that you can assume the reader of your assignment knows, but which may not necessarily be known to the general population. Examples of this may include:

The realist theory in international politics emphasizes the balance of terror between states as a peacekeeping factor. (This is generally known among political scientists.)
There is a difference between litotes and hyperbole (This is generally known among literary scholars.)

Since the target audience for academic texts is fellow experts in the field, you do not need to reference and cite such discipline-specific general knowledge. What is considered general knowledge varies from field to field and between different levels; what is discipline-specific general knowledge for a professor may not be for a first-year student. If you are unsure if something can be referred to as "discipline-specific general knowledge", you should ask the instructor or refer to the source you obtained the information from. This will prevent you from being suspected of plagiarism because you have failed to cite the source.