Books in Primo are assigned Library of Congress Subject Headings. In many ways, subject headings are a form of tagging, in that they represent the content of the material and provide ways for you to efficiently locate more materials that are conceptually related. 

Here are several examples of the various ways you can use LCSH to help pinpoint what you need:

Environmental ethics

Environment -- Philosophy

Environmentalism - Moral and ethical aspects

By consulting book reviews of the scholarly works you are reading, you can gain a better understanding of the place of a particular work within the field.  Here are a few tips for locating book reviews:

• Check to see when your book was published. If it was published more than twenty years ago, and you aren't finding reviews online, you may need to look beyond online sources and check print indexes.
• If you're having trouble finding a review, check with a librarian for help and to cover all your bases, but remember that some books are never reviewed. If that's the case, think about what that might mean about the book's scholarly importance.
• In many databases, you can specifically limit your search results to just reviews.

For philosophy books, start with the resources below and branch out as needed.

Search by the title of the book, or by the author of the review and a keyword from the title. Remember to limit your results to just reviews if available.