Basically I agree – for search engine optimization it can be very useful to have a machine (and human) redable category name in your url. As John Conde points out it also helps you, your visitors and search bots to categorize your content.
But I would strongly recommend to have a hierachical url structure – which does not seem to be the case in your example.
And maybe you could also leave the "articles" out or find a better content related title for that directory like "gadget-news/" or "concert-reviews/" or whatever siuts your content best.
So instead of
use something like this:
or if you/ your cms needs the article ID you could just append it to the slug
This way your url structure would also be quite similar to a corresponding breadcrumb – which could also be handy at some point.
ps: If you just have one main category that's fine – I just used that term instead of "subject" or "theme" because it suits the idea of ordering content in a hierarchical structure.