I suggest.
I desire the information in this book so that I can add to my knowledge of history for the period from 1940 to 1980.
If your love of history(or a subject) is strong enough it is a fine purpose when your purpose is to expand that knowledge base.
However if you were studying history and you don't exactly care about history (or the subject) then building a knowledge base as purpose often isn't motivating enough to get you to activate the book with solid mind probing questions. Your real purpose would be to get thought the exam with a good passing grade or statisfy another outcome or goal.
Alex
[This message has been edited by Alex K. Viefhaus (edited April 25, 2005).]
