"Ethics, copyright laws, and courtesy to readers require authors to identify the sources of direct quotations and of any facts or opinions not generally known or easily checked" .
What is plagiarism:
According to BC's policy on Academic Integrity:
Plagiarism is the act of taking the words, ideas, data, illustrations, or statements of another person or source, and presenting them as one's own. Each student is responsible for learning and using proper methods of paraphrasing and footnoting, quotation, and other forms of citation, to ensure that the original author, speaker, illustrator, or source of the material used is clearly acknowledged. 
"[Citation is]... how you bring your unique gift to the table so that all of us are enriched" .
"Citations were the web before the web. They're the reason we have collective knowledge" .
Are you anxious about plagiarizing accidentally? You can stop worrying if you:
1. Chicago Manual of Style, 15th edition (Chicago : University of Chicago Press , 2004), 594.
2. "Citing Your Sources" University of California, Berkeley Library, last updated February 28, 2013, http://www.lib.berkeley.edu/instruct/guides/citations.html.
3. "Academic Integrity: Policy and Procedures," Boston College University Catalog for Undergraduate Students, Accessed April 12, 2012, http://www.bc.edu/publications/ucatalog/policy.shtml#integrity.
4. "Academic Integrity Tutorial," Boston College, Lynch School of Education, online resource, Fall 2012.
5. John McDargh, BC Assoc. Professor of Theology, in "Academic Honesty Tutorial"