Continuing from the past page with rules on building, hammering and boring a hole on Shabbat: specifics and a principle:
THIS IS THE GENERAL PRINCIPLE: WHOEVER DOES WORK ON THE SABBATH AND HIS WORK ENDURES, IS CULPABLE.
So along with the concept of enduring (that is not necessarily “completing” – but to a point where it is meaningful on its own) we come to writing:
HE WHO WRITES TWO LETTERS, WHETHER WITH HIS RIGHT OR WITH HIS LEFT HAND, OF THE SAME DESIGNATION OR OF TWO DESIGNATIONS OR IN TWO PIGMENTS, IN ANY LANGUAGE, IS CULPABLE.
Now, as to the nod to left handed people – it is my opportunity to be righteously indignant. The Gemara refers to right handed writing as the “usual” so why even bother talking about left handed writing? Just let the left handed person conceptually switch: “Then let his left hand be as the right hand of all [other] people, and so let him be liable on account of his left, but not his right hand?”
No – he’s actually left handed!
But enough of that. The question really is, what is a “completion” of writing? Writing one letter (or mark) is not because it cannot stand on its own. Two letters have at least the potential of carrying meaning for two reasons: a mark indicating alignment, or abbreviations of words.
SAID R. JOSE: THEY DECLARED ONE CULPABLE [FOR WRITING] TWO LETTERS ONLY BECAUSE [HE MAKES] A MARK, BECAUSE THUS DID THEY WRITE ON EACH BOARD OF THE TABERNACLE, TO KNOW WHICH WAS ITS COMPANION.
That is, some kind of an alignment marking: A – A, for example, written when the boards are in place, so that they can be reassembled correctly later.
R. JUDAH SAID: WE FIND A SHORT NAME [FORMING PART] OF A LONG NAME: SHEM (two letters: ShM) AS PART OF SHIME'ON (ShMoN) OR SHEMUEL (ShML) (several other examples follow)
So even though the goal of writing a longer name is not completed, the act of writing a shorter name (even if inadvertent) is.
So these two letters "endure" as they carry meaning. Thus the power of the written word!