Is the fun fact appended to the 又〜も grammar point, which deals with the relative etymologies of 又 and 叉, factually accurate, strictly speaking?
The origin of 又 appears to be a drawing of a hand, per the Outlier Character Dictionary, which in turn cites 古文字譜系疏證. This matches its original meaning in Chinese, which is "right hand.”
The origin of 叉 appears to be a piece of food held in a hand, reflecting its original meaning, “to hold an object between one’s fingers” (this time citing 李學動’s 字源). This character then came to be used for “fork,” as in the utensil, and then finally metaphorically for roads or rivers that split.
The text of the fun fact as it currently stands is this:
The kanji 又 and 叉 share an interesting relationship. 又 is used to refer to things that reach a point of separation, but then fold back on themselves (being translated as ‘again’, or ‘in addition’). On the other hand, 叉 refers to things that reach a point of separation, and then split (being translated as ‘a fork in the road’, or ‘crotch’).
I find this passage very confusing. The kanji “又” was borrowed to mean “repetition or continuation” as early as Classical Chinese, the sense of “furthermore/in addition” is already attested to in Middle Chinese (4th-11 century CE). While Japanese certainly uses kanji in different and creative ways, it strikes me as odd to claim that the sense of “in addition” is derived by metaphor from the actual meaning of “[to] reach a point of separation, than fold back on themselves.” 又 meaning very straightforwardly “again” is probably older than the Nara period!
While I’m all for mnemonics that ignore etymological accuracy to help explain and retain information, I’m not sure how this passage, in its current draft, furthers a learner’s understanding of the usage of また in modern Japanese. This particular point, また …(も), is used as a logical connector in Japanese analytical/academic writing all the time as a straightforward calque of “in addition,” with no particular nuance of separation or folding together. One reference book I own (留学生のための論理的な文章の書き方) lists 又/また as a synonym for 更に, a common usage that would really confuse someone trying to use this mnemonic.
I’m also not sure how useful it is to compare 又 and 叉 at the N3 level in the first place, given that the latter is an unusual Jinmeiyō kanji. Regardless, the latter does not refer to “things that reach a point of separation, and then split;” it refers to things that look like a fork. Because 叉 meant fork and still occasionally means fork in both Chinese and Japanese (叉燒/Cha Siu probably being the big one in common).
Admittedly, perhaps the case can be made that the また of 又 and the また of 叉 share an ancient proto-Japonic root, as both readings are kunyomi. But the above passage specifies that it is referring to the kanji of the words, which I think the evidence for is really weak.
Since this passage is unsourced, I can’t know exactly which authority it’s drawing this information from. But, regardless of source, I don’t think this claim as it is currently written holds up. I really hope this passage can be flagged for a rewrite, edit, or deletion as the mod team finds appropriate. And users with opinions or more information on this passage are welcome to reply with their thoughts!