Q: I can’t recall seeing any discussion on the two usages of “might” in “It might happen if I try with all my might.” Care to discuss?
A: This may surprise you. The verb “may” and its past tense “might” ultimately come from the same prehistoric ancestor as the noun “might.”
So the two forms of “might” in your example (“It might happen if I try with all my might”) are relatives.
Etymologically, the auxiliary verb “may” means to have power, while the noun “might” refers to power itself.
The common ancestor of these words is magh-, a reconstructed Proto Indo-European base meaning to “be able, have power,” according to The American Heritage Dictionary of Indo-European Roots.
That prehistoric root gave birth to the ancient Germanic ancestors of the verb “may” and the noun “might.”
The ancient Germanic magan (to be able), for example, gave Old English magan, the early infinitive form of “may,” while the ancient Germanic mah-ti (power) gave Old English miht, the early form of the noun “might,” American Heritage adds.
(The reconstructed prehistoric forms are rendered somewhat differently by different etymologists, and the early spellings in Old English manuscripts vary.)
In early Old English, according to citations in the Oxford English Dictionary, the verb “may” had three primary uses:
(1) as an intransitive (or object-less) verb, meaning to be strong or have power or influence, (2) as an auxiliary with a bare (or “to”-less) infinitive expressing the power or ability to do something, and (3) as an auxiliary expressing possibility.
Later in Old English, the OED says, the verb developed several other senses, including (4) as an auxiliary to ask for or grant permission to do something.
Senses 1 and 2 died out in the early 1600s, according to Oxford citations, while 3 and 4 are among the primary uses today for the verb “may.”
The earliest OED example for sense 1 (a full verb meaning to be strong) comes from the Vespasian Psalter, an illuminated manuscript from the 700s, with the Psalms in Latin and Old English:
“Exurge domine non praeualeat homo : aris dryhten ne meg mon” (“Arise, O Lord; man should not be powerful”). We’re translating the Old English here. The King James Version translates the Latin as “Arise, O Lord, let not man prevail.”
The first Oxford example for sense 2 (an auxiliary verb used to express the power to do something) is from Rituale Ecclesiae Dunelmensis, a manuscript from the early 800s that describes the liturgical services in the Diocese of Durham in northeast England:
“Gif men færlice wyrde unsofte oððe sprecan ne maege halga him ðis wæter” (“If he has been speaking quickly and harshly, one may not bless him with this water”). Here, maege (Old English for “may”) is being used in the sense of “can” (be able, or have power, to do something.)
The oldest OED example for sense 3 (an auxiliary used to express possibility) is from the Anglo-Saxon Chronicle, a collection of Old English writing from the 800s:
“On ðara Deniscena healfe wearð ofslægen Eohric hira cyng & Æðelwald æðeling … & swiðe monige eac him þe we nu genemnan ne magon” (“On the Danish side their king Eohric was killed, and the atheling Æðelwald … and many others that we may not name here”). The obsolete term “atheling” refers to a prince or other member of a noble family.
And the oldest Oxford citation for sense 4 (an auxiliary to ask for or grant permission) is from “Judgment Day I,” a poem in The Exeter Book (circa 940), a collection of miscellaneous Old English writing:
“Oft mæg se þe wile in his sylfes sefan soð geþencan” (“Often a wily mind may let you decide for yourself what’s right”).
As for the noun “might” (maehte in Old English), here’s an example from the Vespasian Psalter:
“Potentiam tuam et iustitiam tuam deus usque in altissimus : maehte ðine & rehtwisnisse ðine god oð in heanisse” (“Thy might and thy righteousness, O God, reach to the most high”).
As for “mighty” and “mightiness,” they’re also relatives, but we’ll skip the etymology, if we may.
from Grammarphobia http://www.grammarphobia.com/blog/2017/03/might.html