You can use the following search strategies to make a keyword search more accurate: boolean operators and phrase searching.
The terms used in Subject Searching are determined by an Information Professional. They examine the item and determine what it is about, and then assign the Subject Headings from a list of pre-determined terms, called a "controlled vocabulary."
A Subject Search will result in very relevant items.
So now you know if you typed in "capital punishment" as a subject search you could get results that include items that also use the words such as "death penalty," "execution," "death row," "lethal injection," etc. in one search