Matt Cutts explains how Google handles queries and ranks results.
Source: Google - http://www.google.com/howgoogleworks
Firm Search Terms: Are likely to be on most pages that discuss your topic, and/or are described in a limited number of ways.
Soft Search Terms: Are less likely to appear consistently on pages about your topic, and/or can be expressed in so many different ways that is too difficult to come up with a good term or set of terms that are likely to find what you need.
Example:
A student is searching for a specific book with a Native American protagonist that also includes gun-runners, witchcraft, and hippies.
Native Americans is risky as a search term, because there are so many different ways to express that concept, depending on the author’s background, social context, and the time during which it was written. Possible related terms include Indian, Native Peoples, First Nations, tribe, and even a specific tribe name, like Navajo, which—besides being undefined by the asker, could have one of many spellings. So, Native Americans is here a soft search term, as likely derived from the asker’s context as from the words of the book’s author.
Firm terms: gun-runner AND witchcraft
Soft term: hippies
Searching Tips
Google Cheat Sheet: Here are some more Google Advanced Search shortcuts.
Complete: Choose a topic and complete searches using the four searching tips.
Free Scholarly Databases
Google Scholar: All Subject Areas
JSTOR: English (Some free content, requires a login)
National Archives: History
Smithsonian Institution Libraries: History
Smithsonian Institution American Art Museum: Art
Scirus: Science
Complete: Using the same search terms from your previous search, complete a search in one of the free databases.
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