This seems obvious at first, but for some reason portions of the industry continue to perpetuate this notion that each and every web designer is a web developer and vice versa. This becomes ever more apparent when browsing leading blog categories. Often the web design category will be largely filled with development related topics. Fundamentally there is nothing wrong with this, but I think we should just call a spade.
This isn’t a contest
Separating these two vocations has nothing to do with the validity of one over the other. Both disciplines require specific talents that take countless hours to practice and control. With that said, it takes a unique individual to be able to conquer both web design and development on a scale equal to a multi-person, multi-skilled team. However, it is fairly obvious why these two services often come in a packaged offer. Each is only half of the toolset used to create a functional website, one dictating form and other dictating function.
The combo designer/developer
If you are looking to interact with a single person advertising themselves as both the designer and developer, be sure you first have a conversation with them about what their lead skill is. If the freelancer is a designer first, for example, they may not have equal strength in their development skills to support certain custom web technologies, E-commerce and CMS’s come to mind.
Find what you need
If you are looking for web design and development, just be sure to know what you are seeking. If a freelancer only advertises they do one of the two, then inquire further to be sure that they are capable of what you need to do. Often enough either the designer or developer will know of other freelance professionals and can make arrangements to bring in another team member.
Why the distinction
Both industries have passed a point of critical mass, sure in the early days of web design and development, the two were inseparable. However that is not that case anymore, each have very distinct learning paths and jobs titles are more often than not separated into two categories: web designer and web developer. Agencies of all sizes are departmentalizing their labor into these two categories, with some overlap of course, often as front-end developer/designers. But as soon as the heavy lifting needs to be done in either category, the specializations shine through and a designer or developer will wear their appropriate hats.