Students are beginning to use this site heavily. It's great for PDFs of complete books no longer under copyright like Marx's Manifesto of the Communist Party. However, I'm questioning the ethics of students using books listed as "previews" on the site. The preview provides some, but by no means the complete text of the book. If a student finds a quote on a page provided, that supports his or her thesis, is acceptable to use that quote and cite the book on the Works Cited page? What are your thoughts?