How are the noun 方【へ】 and the particle へ related?

Question

I looked up the etymology of　古【いにしえ】 on gogen-allguide, and found the following:

いにしえは、「去る」を意味する動詞「いぬ（往ぬ）」の連用形「イニ」に、過去を示す助動詞「キ」の連体形「シ」がついた「イニシ」が、方向を表す名詞「ヘ（方）」を修飾した「往にし方（いにしへ）」。

This basically says that we take the verb 往ぬ, conjugate it, add the 助動詞 「き」, conjugate again, and finish by adding the noun 方【へ】. This was a bit surprising to me, since I've never seen the noun 方【へ】 myself, and was expecting the particle へ to show up there instead.

This is obviously suggestive of some sort of relationship between the noun 方【へ】 and the particle へ. So - what is the etymological relationship between the noun 方【へ】 and the particle へ?

Answer 1

Put simply, the particle へ is derived from the noun 方{へ}.

Bjarke Frellesvig provides a brief explanation in his book A History of the Japanese Language (page 132).

… The noun pye "side, direction" was being grammaticalized as an allative case particle pye, but in the Old Japanese period had not yet acquired that status.

As for pronunciation, sound changes would have likely proceeded something like *pye > *pe > *ɸe > *we > e.

Answer 2

As ファルキエッレ stated, the particle へ is cognate with the noun, variously spelled 方 or 辺, and probably derives from it. This has been a very productive noun, appearing as a component of many terms in modern Japanese:

• 芦辺 ashibe, "reed-covered bank"
• 海辺 umibe, "seaside"
• 夕べ yūbe, "last night, yesterday evening"

Some modern JA terms aren't necessarily even recognized as compounds:

• 前 mae, "front", compound of 目 + 辺 "eye-wards; visible place"
• 家 ie, "home", probably a compound of 寝 + 辺 "sleeping place"

This へ may also be cognate with 瓮 (he, "container"), from which we get 鍋 nabe, "pot", compound of 肴 + 瓮 "side-dish container".

Regarding the use of へ as a particle meaning something like English "to" or "towards", we already see such usage as long ago as in the Man'yōshū poetry of no later than the mid-700s:

• Poem 3696:
  新羅奇敝可 伊敝尓可加反流
  Shiraki he ka / Ihe ni ka kaheru
  I'll go back to Silla [the kingdom in the north of the Korean peninsula] or to home...

Perhaps in reflection of the noun's sense of "place, general area", the particle へ in the ancient texts denoted "towards, in the direction of" rather than denoting a specific arrival location, and was more often used to indicate faraway places rather than anywhere close by. In contrast, に was used to denote a specific arrival location and was used for closer places. The vaguer connotations of へ ("in the direction of a place") still persist to some extent in modern Japanese and contrast with the more specific connotations of に ("specifically to a place").