Couches Are for Napping
The word “couch” has a more casual sense about it than the word "sofa," probably because of the origin of the term. It comes from the word “coucher,” French for the term “to lie down.” The popularity of couches rose in the Victorian era, maybe because fainting couches became all the rage. They were typically used by women and found in a special room called a fainting room. Women would retire to these rooms to lie down when they felt faint or unwell.
These couches usually had a tapered back, no armrests, or maybe just one, more like what we consider a chaise today. They were generally more casual in form and function than a sofa. Our modern big, fluffy couches are rarely without arms and are more likely to be something you curl up on, take a nap on, and let the dog sit on.
It is also more likely to be smaller than a sofa, comfortably seating 2-3 people. Despite its name, the Fountain Gray Power Reclining Sofa with plush pillows is perfect for a casual family room or den. You can just imagine napping in its depths with your dog curled up at your side.
These features make couches, at least in theory, more informal and casual pieces. And while these two pieces serve the same function, people tend to use the word couch when they are talking about a casual, un-stuffy room.