The Greek letter sigma (σ) has a different form (ς) when used at the end of a word. This distinction seems unnecessary to me, and it's not clear why it would emerge. Do we know why and when this distinction came to be? Was there a benefit for making this distinction? Does the evolution of the character or the literature explain how we ended up having two forms? This distinction seems to only appear in lowercase text, but I am not sufficiently familiar with the evolution of the Greek alphabet.