As an interior designer, I am frequently asked about the defining differences between an architect, an interior designer, and a decorator.  It is an insightful question because the distinctions can be so subtle, yet radical, as to make all the difference between the intended and finished project.  So, to begin... 

DECORATORS: The decorator deals with embellishment and enhancement; that is, they are mainly preoccupied with interior finishes and existing surfaces.  In a way, they add life to a space, creating a three dimensionality that is achieved through their beautification. Typically, a decorator works only with surface decoration such as paint, fabrics, furnishings, decorative lighting, and materials.  They also design drapery treatments, specify carpeting and rugs, wallpapers, accessories, and most soft items.  For the most part, decorators do not have, nor need, a formal design education.  While they do deal with tradesmen, such as painters and wallpaper hangers, their responsibility is limited to the degree to which they can read,  interpret, or create drawings.  So that, they do not move walls, lower ceilings, or add any structural enhancements to the space.  They are typically concerned with aesthetics, style, and mood.  For example, if you want to refurbish your home but decide that you like the given plan and feel of the space, with no desire to change or move anything structural, then the services of a decorator will be all that is required.  Caveat Emptor: because a license or specific kind of professional training is not necessary to the Decorating trade, workmen, such as upholsterers, carpenters, and painters, oftentimes claim to be decorators as well.  They convince the public that they will save money in using their so-called free services.  In addition to very limited resources, tradesmen have limited ideas about design.  The client ends up paying more for less. 

INTERIOR DESIGNERS: Interior designers deal with form and function, space and aesthetics.  In addition to performing all the services of a Decorator, they are professionally trained to create pleasing environments through interior space manipulation and planning.  Qualified through education and experience, an interior designer can identify, research, and creatively resolve design issues.  They can reconfigure interior space to make it workable, meeting the specific needs and wants of the client.   In addition, interior designers also perform the following functions:  the allocation, organizing, and arranging of a given space to suit its function; the design of lighting and its specification (cove lighting, down lights, etc - the type of lighting that involves dropping or raising ceilings) and/or the design of light fixtures; the monitoring and management of construction and the installation of the design; the selection and specification of plumbing fixtures, furnishings, products, materials, hardware, and colors and how all relates to the space designed; the design and supervision of fabrication of custom furnishings and details and their workability; the development of documents and specifications relative to interior spaces (manuals and schedules delineating the plumbing, finish, hardware, paint, lighting schedules); the consulting services to help a client determine project goals and objectives.  In effect, they mediate between the Decorator and the Architect, wedding the disciplines together in a harmonious way.  

ARCHITECTS: Architects typically deal with the structural aspects of a space. I say typically because until the later part of the 20th century, most architects built buildings or houses.  More recently, however, architects have extended their domain to include interior apartment renovations, encroaching somewhat onto the designer's territory.   Like the interior designer, architects mold and manipulate space to create aesthetically pleasing and well functioning homes or offices for the client.  The major differences between the interior designer and architect lies in the architect's education, training, and experience and in their ability to build from the ground up, creating new structures.  They are not trained and customarily not interested in the finishing of a space, that is, it's decoration. However, a good architect can combine all three skills, creating a comprehensive work of art.  Typically, architects are more interested in the creation of large structures such as office and apartment complexes, restaurants, shopping malls, office buildings, museums, houses.  The residential architect, in particular, can be very masterful in creating a satisfactory built environment, inside and out.  But this is more the domain of the "design architect," one whose interests veer towards combining great design with great structure.  They are interested in the implementation of a master plan and the outfitting of its interiors.  Architects are also knowledgeable about the mechanics of finishes and materials, the how and why things structurally work the way they do, and the surrounding environment's relationship to their creation. Ironically, while the most educated of the three professions, architects are the least compensated for their skills. 

CONTRACTORS:  Contractors implement the design drawings of the architect and designer.  They bring the design professional's vision from a two-dimensional drawing into 3 dimensional reality.  As such, they physically build the space and bring to fruition the final design phase.  Working with either a decorator, designer, or architect, the contractor takes his direction from their aesthetic directives.  A really good contractor will be able to facilitate the attention to detail and quality workmanship necessary for an excellent project.  Caveat Emptor:  Contractors do NOT design; they build.  They work in tandem with the design professional to bring into being their vision.  They do NOT choose colors, fabrics, finishes, design kitchens, baths, rooms, etc.  If a client chooses a contractor in place of an interior designer or architect, they cut out the most vital step of the design process: the vision, the creation, the style, the taste.  For instance, in designing a bathroom a designer will select tiles, choose and decide on the proper placement of fixtures, fittings and accessories,  design the tile patterns, select the color and texture of the walls and all the other design decisions necessary for the successful fruition of the space.  Often, a contractor will say he performs these duties as means of procuring a project, cutting out the services of an architect or designer.  However, the customer needs to be aware that the contractor's expertise is in the implementation of a design, not in its creation.  In addition, when a contractor performs an architect's job, he removes a checks and balances system, so vital to the consumer.  That is, without the presence of a design professional, the ability to check the accuracy of the tradespeople's work is missing. There is no one to call the contractor on his precision or attention to detail.  

The best projects combine the skills and abilities of the Architect, the Interior Designer, and Decorator.  It is rare, however, to find a firm or individual who can successfully bring all three skill sets into play.  Josef Hoffman, Charles Rene Mackintosh, Robert Adam,  William Morris, Rossetti, Frank Lloyd Wright, and Le Corbusier are among those icons who have done such, designing beautiful environments inside and out. More common is the confrontation among the three, rather than their seamless integration. When the designer or decorator places furniture incongruous to the structure, or when the architect designs space without consideration or respect as to how the furnishings will be laid out, then the client suffers. The good news is that more and more design professionals are teaming up, creating comprehensive design alliances, to better serve their clients.  In essence, the challenge for the decorator, interior designer, and architect ultimately lies in their ability to seamlessly marry great form to function.