Of the 500 or so images I've created during my MFA program, 80% are in done in a square format. Of the many critiques I've participated in, I've been ready with a thoughtful answer to the question..."so why are you painting in a square composition?"
Yet, no one in the past two years ever asked me or challenged me on why I was painting in a square format. The first problem an artist needs to address before beginning a work, is what size and shape the work will be. The shape of the frame an artist chooses influences the final image and reveals something about that piece of art work.
I consciously choose a square format as I think of the square as a unit, a part of a whole, that has the same properties whole as it does in its parts. It makes up a grid and is considered emblematic of modernism. Square compositions can be both complete and incompleted, as you can always add another square to an already existing one.
A square format does not favor the dynamic vertical or calm horizontal plane, it is stable and supports the image in equanimity. The equal sides allow the image to be, without too much input from the frame. It is a simple, regular and familiar geometry. In Socrate's Meno, doubling the square, he says "This knowledge will not come from teaching, but from questioning, he will recover it for himself." Guess there are some questions you just ask yourself.