[BetterRed]

@commandante - pretty sure - create a User Category called Philosophy, add relevant Authors - e.g. Immanuel Kant, Thomas Hobbes, Peter Singer, John Locke etc - to it. There has to be a book by the author, you could create 'empty books' as place-holders for Philosophers whose works you don't yet have.

Search on @Philosophy will find all the books you have by those authors, and when you add Peter Singer's "The Most Good You Can Do" it would, by definition, show in that search, which could be Saved or used to create a Virtual Library.

Added : the English version of calibre uses the words 'tag' and 'category' interchangeably - hence Tag Browser, the top level items of which (Authors, Publishers, Saved Searches and Tags) are collectively referred to as 'categories'. I don't recall seeing the term 'label' used in the product nor in the doco.

BR