Reference resources are a great place to begin your research. They can help you define terms as well as to find basic information about a topic, a chronicle of its history, theories, key people and sometimes a bibliography of additional sources.
There are many different types of reference sources, which include dictionaries, encyclopedias, thesauri, bibliographies, handbooks, style manuals to name a few.
Oxford Handbooks Online (Philosophy Collection)
Published, by Oxford University Press, the Handbook series contains in-depth, high-level articles by scholars at the top of their field. Consult the list of recommended readings at the end of a relevant article to locate more sources on the topic you are researching.
Oxford Bibliographies Online
Bibliographies like Oxford Bibliographies offer authoritative research guides helping you to narrow the vast number of citations to the best scholarship on a given topic. Includes subject collections in Classics and Philosophy.