Is one to do with visuals and the other with content?
An article published "Creative Director vs. Art Director":
Creative Director's Key Role
The creative director typically thinks through the early phase of the
project to develop the concept. This director oversees the entire
team, which includes the copy chief, photographer and art director.
Many creative directors ultimately work their way up through the ranks
to become partner or CEO. The creative director generally has the
final say on what gets delivered to the client. This vital position
nurtures the studio or agency's talent and also steers its design
Art Director Key Role
An art director executes a strategy, concept or idea provided by the
creative director. After the concept has been created, the art
director is generally responsible for the stylistic look of the ad or
design. He brainstorms with workers and provides direction and
inspiration to the staff, which includes the graphic designer, sketch
artists or typesetters. The art director helps maintain brand
consistency. He oversees the project through the production department
and other phases, including prepress and printing. The art director
may have the final approval for delivery of the project if there is no
The creative director relies on intuition and creativity to get the
job done. He understands the psychology of advertising and works to
create an effective vehicle for reaching consumers. Although a
creative director's forte is not necessarily his technical skills, he
can write copy, design logos or choose typefaces, if necessary. The
art director relies on his technical skills to execute the project.
Both roles complement each other.
Education and Pay
Both creative directors and art directors need at least a bachelor's
degree in advertising, fine art or design. Creative directors may
continue their education to prepare for the best job opportunities.
According to the Bureau of Labor Statistics, the median salary for art
directors in 2010 was $80,600 per year. In comparison, a creative
director's median salary was $125,000, according to a 2011 AIGA/Aquent
Survey of Design Salaries.
Source of the article from chron and there has been a discussion on the topic at Graphic Design Forum here ages ago.
Are they more or less interchangeable?
Art Directors at bigger studios or corporations often oversee just a particular segment of design or at least different teams. So you might have an art director for interactive design and another for package design. The Creative Director would oversee all these.
Do they have different responsibilities?
Can you have both in the same shop?