What’s the difference between studying a subject extensively and studying it intensively, between doing extensive research and intensive research? It seems like a simple enough question, one that could easily be answered by consulting a dictionary. I consulted four: Merriam-Webster Unabridged (3rd ed), The New Shorter Oxford English Dictionary, Webster’s New World College Dictionary (4th ed), and The American Heritage Dictionary (5th ed) .* Here’s what I found: