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.
2In Arabic most letters have four different forms depending on position (initial, medial, final, isolated.) I have no sources, but this seems natural to me, and more natural the more handwritten the alphabet is. In handwriting you naturally tend to make letters slightly different if they are at the beginning or end of a word (or following an "o", for example.) Although in Greek letters are separate from each other, letters are sinuous, (especially sigma) and I see no reason not to suffer such changes along centuries– RafaelMar 22, 2018 at 12:07
Thompson 1912 mentions the following on page 189:
Not a full answer but at least something to start with.
3(+1) Excellent quote concerning the tendency to write final sigma differently. For those who haven't seen the text which Thompson is talking about, I thought it good to point out that the uncial sigma doesn't much resemble the modern forms. The word ισως looks like ιcωc, the sigmas appearing as C, both in the middle and at the end. The main difference is that the final C appears top-heavy; i.e. the upper part of the C extends downward. Looking at Thompson's texts, I would say that the modern forms don't start to appear until around the 14th or 15th centuries. (see e.g. pg. 264) Mar 23, 2018 at 13:31
1@PédeLeão BTW, C-like sigma is called "lunate sigma", and is ancient– RafaelMar 23, 2018 at 16:38
I quote https://www.reddit.com/r/asklinguistics/comments/uzypjj/why_does_lower_case_sigma_have_a_different_form/iaeq7f1/.
The oldest form of sigma is Σ, as found in inscriptions. In manuscripts, this was often simplified to the so-called "lunate" sigma, resembling the Latin letter C. (This is also found in Cyrillic).
When a scribe was writing connected script, the lunate sigma would be realized as σ, allowing the writer to continue to the next character without lifting the pen. At the end of a word, a small flourish was added to give ς.
1Welcome to the site! This sounds reasonable, but do you happen to have a reference (such as a book or an article) to back it up? That would make the case much stronger.– Joonas Ilmavirta ♦May 31, 2022 at 9:16