Views Arguments Question

Hey,

Thanks for reading. I'm developing a site that's going to list books about certain causes, i.e. global warming, poverty, etc. It will have pages like "environment" and then sub-pages for causes within that category, i.e. global warming, logging, etc.

I want to create a single view that will list an unfiltered list of these books for the "landing page" (i.e. environment page) and that will then filter them depending on the url (i.e. environment/pollution/books will take you only to books about pollution). I was able to do this by adding a taxonomy term argument but the problem is that it made environment/pollution take me to pollution books as well as environment/pollution/books. I need the url: environment/pollution for another page and so I cant have this view display anything at that url.

So what I need is to create like an "empty argument"; that is, create a url like environment/logging/books where LOGGING does not take you to any view but the adding /books does. How do I do this?

thanks again,

Fernando