The quote from Jimmy Wales, founder of Wikipedia, comes from an article in the Chronicle of Higher Education, “Wikipedia Founder Discourages Academic Use of His Creation.”
The same can be said of the dictionary – I find it hard to believe that I get students starting essays with “Webster’s Dictionary defines…” – or worse still, “Dictionary.com defines…”
The reason, in both cases, is that encyclopedias like Wikipedia, and dictionaries, are repositories of information which are the conclusions drawn by experts on a given topic or language.In university, students need to be going behind the scenes. They need to be able to explain why a dictionary might define a word a given way, and why certain authors advocate for a particular understanding of a word. They need to be able to explain why an encyclopedia says that event x happened in place y on date z, what the evidence is that leads historians to that conclusion.
Wikipedia and Dictionary.com have issues of their own, since they don’t reflect the kinds of expertise that one might legitimately hope for in other encyclopedias and dictionaries. But in general, while dictionaries and encyclopedias can be a useful first point of departure in research, the expectation is that you will go further and deeper than such sources can take you.