Etymonline doesn't expound how:

  1. for þon þy shortened to only 'for'.

  2. 'for' persisted in meaning because. 'For' is a function word that means many meanings, and 'for' alone doesn't intutively mean 'because'.

To wit, in omitting þon þy in for þon þy, you're eliminating the content words that impart the meaning of "because" to for þon þy. But why didn't eliminating "þon þy" eliminate the meaning of "because" in 'for' too?

For alone as a conjunction, "because, since, for the reason that; in order that" is from late Old English, probably a shortening of common Old English phrases such as for þon þy "therefore," literally "for the (reason) that."

  • 5
    Similarly, I imagine, to how pas came to lean not in French, even with the significant ne omitted forum.french-linguistics.co.uk/forum/topics/3179028:Topic:1681
    – Unrelated
    Commented Mar 30, 2020 at 4:45
  • you are more likely to find an answer in a question about the synchronic grammar, w.r.t. pondering whether "'for' alone doesn't intuitively mean 'because'". Indeed, you cannot indiscriminately exchange the two, so your question seems to insinuate a wrong premisses.
    – vectory
    Commented May 3, 2020 at 18:51
  • Diachronicly, it might be worthwhile to cp. German denn, which developed out of a similar form. It's not to be confused with dann "then", though related, and not "than" either. Basicly, it does not translate, so the comparison is of little value unless you are interested in older layers of the languages. Comparing da is probably overkill.
    – vectory
    Commented May 3, 2020 at 19:00

2 Answers 2


A not insignificant role might have played forth. The first to quotes in wiktionary on OE forth do looketh like a fixed collocation that fell out of use and appeared in context of entailment. My first thought had been that an univerbation forth-thon (thy) might simply loose the ending of thon under the setting-in erosion of middle english morphology. The second thought is, that it might appear like for it, which is a frequent collocation now. So I went forth, didn't exactly find confirmation, but see for yourself:


  1. expresses the continuation of an action

late 10th century, Ælfric, "On the Festival of St. Peter the Apostle"

Petrus cnocode forþ oþ þæt hīe hine inn lēton.

Peter kept knocking until they let him in.

late 10th century, Ælfric, "On the Festival of Saint Peter the Apostle"

Hīe ēodon forþ oþ þæt hīe cōmon tō ānum wīċe.

They kept walking until they came to a street.

9th century, Bald's Leechbook vol. I

Drince hē forþ þone drenċ fēowertīene niht.

He should continue to drink the potion for fourteen days.

You'll note that "until" can be well replaced with "for" in the first example. It's not obvious why that should occur; after all, forth still exists. It has lost this meaning particular meaning, but one would expect the morpheme had been recognizable--in contracted speech it might have been confused, perhaps.

It is by the way notable that oth thaet had carried most of the conjunctive force, which neatly parallels German auf dass "for that, so that" (wherein auf "up, upon" might have been informed by ob, if, insofar there can be no notion of unbroken descent in view of the wide divergence between conjunctions and prepositions in the various Germanic lects). I cannot find an etymology, nor a continuation, for oth "on, until" right now, only an instrumental suffix -oth, and of course until, which has a cognate in the Hittite language (for example) and in English and.

It goes without saying that close and distant relatives of for had often been used in conjunctive phrases, though I'm not aware of it being used alone like that.

Of course, if it was all an accident, the explanation would have to be more involved. Vice versa, if there's no


All from OED

for, prep. and conj.

Etymology: Old English for preposition = Old Frisian, Old Saxon for , Gothic faur ; probably a shortened form of Germanic fora fore adv. and prep., arising independently in the various languages.[...]

The use of for as a conjunction has not been found earlier than the 12th cent. The older language supplied the place of the conjunction by locutions in which for preposition governed a neuter demonstrative pronoun followed by a relative particle: for ðon ðe , for ðý ðe , etc. (see for-thon conj., for-thy conj.). The conjunctional use of for = for ðon ðe may be explained either as an extension of the functions of the preposition to govern a noun-sentence, or as an ellipsis.

In Old English for and fore seem to have been used indiscriminately as prepositions; in Middle English they were gradually differentiated.

For 21. Because of, on account of:

a. a person or persons.

c1000 Ælfric Genesis xx. 3 Þu scealt sweltan nu Abimeleh for þam wife þe þu name.

b. a thing. Also in for cause (see cause n. 6) and after such nouns as charge, reputation, etc., and adjectives as sorry (see those words). Some adjs. formerly construed with this preposition now take others; e.g. glad of.In Old English for with the instrumental case of the neuter demonstrative pronoun formed adverbial phrases = ‘therefore’, which, with the addition or ellipsis of the relative ðe became conjunctional phrases = ‘because’. (For these phrases and their later representatives see for-thon conj., for-thy conj.; cf. also forwhy conj.). Similarly, for that conj. appears from 13th cent. as a conjunction; and in the 16th cent. there are a few examples of for this in the senses ‘therefore’ and ‘because’.

a1555 J. Philpot tr. C. S. Curione Def. Authority Christ's Church in R. Eden Exam. & Writings J. Philpot (1842) (modernized text) 396 For this [L. igitur], Florebell, thou hast a high bishop and ruler of the church such a one peradventure as thou soughtest not after.


1849 T. B. Macaulay Hist. Eng. I. 308 Notorious both for covetousness and for parsimony.

for þon þy = for then which - "He could not lift it for then [of] which it was heavy >

because is a contraction of "by [the] cause [of]" - "he could not lift it by the cause/reason [of] it was heavy

because, adv., conj., and n. Forms: ME–16 bicause, bycause, ME–15 by cause, (15 be cause), ME– because; dialect 'cause.

1. Followed by that or why: For the reason that. (Formerly for was sometimes prefixed.) archaic. Also because why used interrogatively, = ‘why?’ (cf. cause why n. at cause n. 3c); chiefly dialect.

c1305 Deo Gratias 37 in Early Eng. Poems & Lives Saints (1862) 125 Þou hast herd al my deuyse, Bi cause whi, hit is clerkes wise.

1887 W. D. Parish & W. F. Shaw Dict. Kentish Dial. 10 Because why, why? wherefore? A very common controversy amongst boys:—‘No it ain't’—‘Cos why?’—‘Cos it ain't.’

1921 D. H. Lawrence Sea & Sardinia i. 12 The painters try to paint her [sc. Etna]..in vain. Because why?

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