Now, you’re probably also want to make some changes to the single post navigation, and make it so that single posts in your special category won’t get posts from any other category in their navigation links. And also, chances are you’ll want to exclude posts from your special category from the navigation links of posts in all other categories.

In other words, in the navigation links of single posts from your special category you’ll only get posts from that category, and in the navigation links of posts from all other categories, you’ll get posts from all categories except your special category. Two separate navigations.

For all of this, all you need to do is use the following two Thematic filters: thematic_previous_post_link_args and thematic_next_post_link_args. If you’re interested to look into the code, you can find the filters being applied in thematic/library/extensions/content-extensions.php

And here’s the code snippet to include in your child-theme’s functions.php:

function custom_previous_post_link_args($args){
	if(in_category(3)){
		$args['in_same_cat'] = TRUE;
	}
	else{
		$args['excluded_categories'] = 3;
	}
	return $args;
}
add_filter('thematic_previous_post_link_args', 'custom_previous_post_link_args');
 
function custom_next_post_link_args($args){
	if(in_category(3)){
		$args['in_same_cat'] = TRUE;
	}
	else{
		$args['excluded_categories'] = 3;
	}
	return $args;
}
add_filter('thematic_next_post_link_args', 'custom_next_post_link_args');

Related posts:

1. Add “Featured Posts” to your Thematic child theme
2. Quickly add a Category DropDown to Thematic 0.9
3. WordPress pieces of code of the month