As people were asking about the value of my books after my recent apartment fire, I decided that value could be determined 3 ways.
(1) Economic. How much would it cost to replace the book? How much did I pay for it originally? Some were gifts, some would be expensive to replicate in that I would have to order them from Spain.
(2) Sentimental. The book is not only a gift, but bears the signature of the author, or a water-color drawing. Or it's a book I've had many years and one that has formed a part of my identity.
(3) Use value. A book I need right now or in the immediate future to do my research.
Obviously these categories overlap but don't coincide completely. The scholarly library is a main part of one's usable scholarly base: it is amassed over years, at considerable expense, cumulatively speaking. A few hundred dollars here, fifty there, ten or twenty there, over a virtual lifetime. There were books ruined that I've had since high school. And one forms sentimental attachments. I felt sick to my stomach when I saw a copy of some particularly prized volumes covered with ash and soaked in water.