Okay i'm having a bit of a catogorisation/taxonomy/filtering problem here and am at loss on how to solve this. 
I hope someone could help me on the way a bit. 

Say I've got a blog about food, with a few main subjects;

 - thai food
 - indian food
 - greek food
 - mexican food
 - french food
 - spanish food
 - fast food

A blogpost is always tied to one or multiple of these subjects (a blogpost about a fajita is just filed under *'mexican food'*, a blogpost on 'burrito' under both 
*'mexican food'* and *'fast food'*). 

Then there are different categories like

 - restaurants 
 - reviews
 - information
 - news
 - take-out
 - recipies

Blogposts are also always tied to one or multiple of these categories. These categories are available through the menu.

What I want to do is, offer the visitor a possibility to filter all the content on a specific subject. If one would chose to put the filter on *'thai food'*, all the articles returned should be about thai food. 
If one would chose the category *reviews* while the filter *'thai food'* is on, it should only list articles about *thai food* within the category *reviews*.

If the filter is set to off (or all) and one would navigate to the category *'reviews',* articles in the category review on all different subjects should be retreived.

So there it is! Now I realize I might have explained this in a difficult way, but I'm a loss on how to achieve this here.

Right now I've got both the subjects as the categories as top level categories but I'm assuming a custom taxonomie might be a better solution. Any help would be greatly appreciated!

*edit: okay to make things easier, I think I have a better idea of what should be happening here: I should detect wether the user has a filter selected (which are custom taxonomies right now) and return posts accordingly. (so something like: if thai food is selected and user clicks on category 'reviews', return a query with custom taxonomie thai food in category reviews) My main question in this case is, how do you detect if there is a taxonomie selected, and which? 
Thanks!*