Why should I use journals for my assignments (and not only books)?
Academic journals are a preferred source of academic information. They usually offer a more current view than do text books, and have credibility due to the process of peer review, under which journal articles ('papers') submitted by researchers are evaluated by experts in the field before being published.
Articles from scholarly, peer-reviewed, academic journals are more credible than articles from popular or trade journals ('magazines') because they have gone through the most rigorous review process. They also have the most references or citations.
