Reference Sources provide you contextual information and an overview of your research areas/topics. These are good for familiarizing yourself with your research area.
Reference sources can:
Provide an overview of your topic
Are often written by scholars or experts in the field
Provide key people, places, events, and terms that you can use to refine your searches
Guide to scholarly literature by field. Subdivided into articles by established scholars covering major categories of research with corresponding bibliographies of recommended resources.
Encyclopedia covering a variety of topics and figures in the history of philosophy.
Major categories include Aesthetics, African and African-American Philosophy, Ancient Philosophy, Arabic and Islamic Philosophy, Philosophy of Biology, Chinese Philosophy, Cognitive Science, Epistemology, Ethics, Feminism, Japanese Philosophy, Judaic Philosophy, Language Philosophy, Latin American and Iberian Philosophy, Law, Logic, Mathematics, Medieval Philosophy, Metaphysics, Mind, Physics, Religion, Renaissance and 16th Century Philosophy, Science, Social and Political Philosophy, 17th Century Philosophy, 18th Century Philosophy, 19th Century Philosophy, 20th Century Philosophy, and Continental Philosophy.
"The Internet Encyclopedia of Philosophy (IEP) (ISSN 2161-0002) was founded in 1995 to provide open access to detailed, scholarly, peer-reviewed information on key topics and philosophers in all areas of philosophy." - https://iep.utm.edu/home/about/