In philosophy, lots of scholarly writing is only available in books or other physical formats, so don't stop with just the journal databases. Use the Books/Media Tab to find books at Lavery Library or other libraries.
TIP: A book usually covers a broader topic than a journal article, so when you're searching the catalog for a book, don't be too specific.
For example, let's say your topic is "David Hume's argument against induction". Try just "David Hume". Once you've got a book in your hand, you can use its index or table of contents to find the parts of the book that talk about induction.