In my terminology what is a relative pronoun which is inclusive of the antecedent in your sentence. A leading figure in the Scottish enlightenment, Adam Smith's two major books are to democratic capitalism what Marx's Das Kapital is to

William R Ward wrote on 02 Jan 2005: William R Ward wrote on 01 Jan 2005: I agree with everything you say here. The rule is ... it stated quite clearly on The Grammar Doctor's website: http://www.geocities.com/grammardoc5/prednom.html