While the terms couch and sofa are now used almost interchangeably in everyday language, they have distinct origins and historical differences. The choice between the words today often reflects formality and regional preference rather than a specific type of furniture.
Historically, the distinction is rooted in the etymology of the words. The word "couch" originates from the French word "coucher," which means "to lie down." Consequently, a couch was traditionally a piece of furniture, often without arms, intended for reclining or lying down, similar to a daybed or chaise lounge. In contrast, "sofa" comes from the Arabic word "suffah," which described a wooden bench covered with cushions and blankets. This piece was designed for multiple people to sit upright and typically featured a distinct back and two arms.
In contemporary use, these original definitions have largely dissolved. The furniture we buy today, regardless of what we call it, is usually a long, upholstered seat with a back and arms designed for multiple people. However, a subtle distinction in connotation remains. Within the interior design and furniture industries, "sofa" is often considered the more formal and precise term. "Couch" is viewed as a more casual, colloquial term that is widely used in daily conversation.
Ultimately, for all practical purposes, there is no functional difference between a modern couch and a modern sofa. The term you choose to use is simply a matter of personal habit or the level of formality you wish to convey.
