Try to use a concordance.
A concordance indicates the location of words in a text. With the help of a concordance you may choose the principal words used in a book or a text. It filters source material for the occurrence of specific words. It is a very time-consuming and difficult work to create a concordance, thus concordance often only exist for major works.
How often did Shakespeare use the words "doth" and "dost", "hath" and "hast" in his works?