C - Is the information current?
R - Is the information relevant/reliable?
A - Who is the author/authority?
P - What is the purpose/point of view?
Popular sources are written for a general audience. They may take specialized or complicated information and 'translate' it so that the average person can understand. Magazines, newspapers, and many websites are usually popular sources. Example of News/Popular Source
Professional sources are written for an audience that consists of people working in a specific field. Professionals may use these sources to keep up with developments in their field and adjust how they do their work. Trade publications and the websites of professional organizations are often professional sources. This guide from another college provides more details on the difference between professional (also called 'trade') publications and scholarly (or 'academic') journals. Example of a Professional Source
Scholarly sources are written for scholarly audiences, and often use advanced vocabulary. They are written by researchers in many different fields in order to share the results of their research. When they directly report the outcome of a study that the authors conducted or observed, they can be said to be empirical. Other kinds of scholarly sources analyze and compare the results of several other research studies, and may be called literature reviews or meta-analyses. This website on the anatomy of a scholarly article from NCSU can help you learn to identify scholarly articles through characteristics they often display. Example of Scholarly Article