られる honorific/polite versus passive origin

Question

Is the られる used as a honorific (some sources use "polite", but I assume it's a honorific?) related to the passive form (perhaps it's alternative usage) or is it something that emerged separately? (would the difference have some potential impact?)

From what I found out:
Passive
https://en.m.wikipedia.org/wiki/Japanese_verb_conjugation
"The passive is used: (...) as a form of respectful language"

https://cotoacademy.com/japanese-keigo/#Honorific
"The honorific style can also be expressed with what is called the “easy keigo” with verbs used in the passive form れる or られる"

https://www.wasabi-jpn.com/japanese-lessons/the-honorific-form-the-humble-form-and-the-polite-form/.l
"Alternative Form: To Use the Passive Form"
"When using the passive form as a honorific form"

http://www.guidetojapanese.org/learn/grammar/causepass#Using_passive_form_to_show_politeness
"using passive form is another more polite way to express an action"

Dictionary of Basic Japanese Grammar
"Passive verbs are also used as honorific expressions"

Versus

Not passive
https://japanese.stackexchange.com/a/651/9719
"Don't forget that there is a third conjugation of this form that is a type of keigo"

Author of Japanese from Zero in discord:
"That is not passive nor is it potential. It is a high level polite."

So no idea who is right. It being a different usage of the passive form would imho make sense as it would follow the politeness through indirectness approach (passive somewhat feels less direct to me) ... and maybe that it seems less likely there would be another conjugation to just happen to end with られる. But I'm not a linguist

Answer 1

One of the primary mechanics for showing politeness and respect in any language is the use of increasingly indirect expressions. Consider the following in English:

• Gimme that
• Give me that
• Please give me that
• It would be great if you gave me that
• It would be great if you could give me that
• It would be greatly appreciated if I could have that
• One would be ever so appreciative if that could somehow make it into one's possession

These are contrived examples, but the basic point is that the more indirect the expression, the more polite it is. The same point is made in the Japanese Wikipedia article on 敬語【けいご】, in the 敬語【けいご】の方法【ほうほう】 section (emphasis mine):

敬語の方法
さまざまな言語に共通してみられる敬語の方法は​[行]{●}[為]{●}[や]{●}[行]{●}[為]{●}[者]{●}[を]{●}[直]{●}[接]{●}[に]{●}[指]{●}[示]{●}[し]{●}[な]{●}[い]{●}[こ]{●}[と]{●}​である。

• 行為者の代わりにその人物がいる場所を指す名詞や指示詞を用いる。
• 人称を変える（二人称を三人称にするなど）。
• 単数を複数にする。
• 格標示を変える（「天皇が」→「天皇陛下におかせられては」など）。
• ​[受]{●}[動]{●}[態]{●}[を]{●}[用]{●}[い]{●}[る]{●}。
• 迂言法を用いる（1語の動詞「読む」を「お読みになる」のように複数の語で表す）。

From what I can find regarding the derivation of the (ら)れる ending, it seems that the initial meaning was one of spontaneous action: action that happens on its own, without an agent (i.e., it just happens, no one does it). The semantic shift from "spontaneous" to "passive" is not that far, nor surprising. Then, as a basic indirection technique, the use of passive forms to indicate politeness and respect is something that Japanese shares with many other languages, so this too is neither a far-reaching nor unexpected shift.

As far as your books go, I think there's some confusion -- I don't think the authors are saying that (ら)れる when used as an honorific is somehow completely separate from the (ら)れる that indicates the passive. I think they're instead just trying to emphasize that this ending has multiple meanings.

Consider the English word get. This can mean to receive: "I get a present." This can mean to become: "I get better." This can create a passive construction: "I get run over." This can mean to understand: "I get what you're saying." Each of these senses are distinct, but the word get in all of these is still the same word. Similarly, the passive, potential, and polite uses of (ら)れる are each distinct, but the ending (ら)れる in all of these is still the same ending. The fancy terms for this kind of multifarious use of a single word or affix are polysemous or polysemic. This is why some dictionary entries get to be so big. :)