Hopefully a simple question. I've added several post thumbnail sizes to functions.php using add_image_size. They are each named exactly like a post category. I would like to find a way of making each post call the specific thumbnail size assigned to it's category.
The best way I can imagine doing it is by inserting the category name into the thumbnail string like so:
<?php the_post_thumbnail( 'INSERT CATEGORY NAME HERE' ); ?>
What could I put in this php string to make it insert the category's name into this?