If you search a catalog or database and receive a large number of results, add a limit or additional keyword in order to retrieve a manageable and relevant number of results to review. At the same time overly narrow search terms can return too few results. One way of solving both problems is to use Boolean operators (AND, OR, NOT), which allow you to limit or expand searches depending on your needs.
For example, a search for Plato AND soul will return items that contain both concepts:
anima OR aesthetic* making returns items that contain either one of the concepts or both:
Germany NOT Finland returns items that talk about Germany but do not mention Finland:
Phrase searching:
An important strategy to use when searching for phrases ("black and white") or titles:
For example, "The Oxford dictionary of philosophy"
will search for those words in that order, finding the book The Oxford Dictionary of Philosophy 
.
Truncation and Wildcards:
Most catalogs and databases enable users to search variations of keywords by using truncation (*) or wildcard (e.g., ?, $, !) symbols.
For example, one could search for politic* to find poltic, politics, political, politicking, and so on.
Wildcard searches are for differences within words: a search for wom?n will return results for woman, women, and womyn.
Nested Searching:
When pairing two or more keywords with another keyword, it is important to "nest" the former terms within a larger Boolean search.
philosop* AND history AND 20th AND ("united states" OR america*) will return results for the union of the three subject areas
Results include: The unraveling of scientism: American philosophy at the end of the twentieth century