Search engines, like Google, search by keyword. The default search in Orbis, Quicksearch, and Articles+ is also by keyword, where you will get results with your keyword(s) located anywhere in the record or document.
A subject defines a book or an article as a whole, and subject headings link information -- just like how hashtags link conversations in social media (#yalelibrary). Using subject headings is an effective way of doing research.
Ways to identify library subject headings:
You can combine your keyword and subject searches by using Boolean operators AND, OR, NOT in an Advanced Search. When combined with keywords and/or subjects, boolean operators will help focus your search in the following ways:
In the example above: