You must acknowledge all the ideas and research of others that you use in your manuscript. However, you do not need to acknowledge common knowledge. Common knowledge is information that the average person would accept as reliable without having to look it up. This includes:
- information that everyone or nearly everyone knows,
- information shared by a cultural or national group and;
- knowledge shared by members of a certain field.
Common knowledge in one culture, nation, academic discipline or peer group may not be common knowledge in another. It is not always easy to decide whether information is indeed common knowledge or not. The general rule is: when in doubt, cite.