Simmel wrote about how doors can separate the connected, what about window?
Window is a funny thing. Its physical property draws a line between the inside and outside, yet people inside can see out and people outside can in. Unlike a door, it somewhat connects the separated private and public spaces. I have this habit (which I am sure most people have) of looking into a house whenever I walk pass one, just to see what is inside that house and imagine myself being in it. But when I am in my flat, I am anxious about people looking in, I feel my private space is being exposed; it has gone public. Somehow, it gives me an odd sense of security because I can see what it is going on outside. I can see my cat playing outside and across the road; I can keep an eye on him. I can see what the weather looks like before I head out. It allows me to get the information of the day I need.
Because of windows, a house is lit up by the natural light flooding in. Every single window in the house frames up a piece of natural painting of the outside world in it seasonal dressing. It is a poetic piece.