This should be simple for the language experts. I can usually find reference to these things, but this one has proven exceptionally difficult.
How did the phrase “have to” evolve to mean “must”?
Taking each word literally, “I have to do something” is nonsensical to me. Unless the word “need” is added. “I have need to do something” does make sense.
Simple? Ha! As far as anyone seems to know, the possessive “have” comes directly from English’s Germanic roots. It appears that the auxiliary “have” (I have eaten Spam) comes from Latin habere; its French and Spanish relatives, avoir and haber, are used the same way. Habere was not used this way, as the perfect tenses in Latin were conjugated. Thus it appears that the imperfect tenses of the Romance languages follow native grammar, rather than Latin’s. The Spanish and French words correponding to “I have to” are related to the English word debt; all are derived from Latin debere, which is derived from de + habere – a debt or obligation is something “had from” someone else (in German, the concept is addressed by the word müsser, related to English “must”).
And, wired together as that is, I think it’s about as close as you’re going to get to an answer. Unless, of course, someone who knows what he’s talking about comes along with the right answer in a book. Feh.
In Olde English, it seems we were more verbose than nowadays. Even more recently, (as anyone who’s ever seen a Merchant Ivory adaptation of Pride And Prejudice can verify) it was considered classy to use more words than necessary:
Then: “Madam, it has come to my attention that my comrade-at-arms is enamoured of your beauty and would be honoured if you would accompany him this eventide to the theatre.”
Now: "My friend thinks you’re hot. Want a date at the cinema tonight? "
In Shakespeare for example, characters may say “I have need to…” / “I have cause to…”
As with the development of most languages, particularly English, laziness of the speaker leads to the dropping of superfluous words… therefore:
I have (need) to visit Ye Olde McDonalds
I have to visit McDonalds
(N.B.: IANALinguist! Can you tell?)
Speaking of Shakespeare, can anyone explain “must needs”, as in “It must needs follow that I like pie”?
It seems that this occurs in Spanish as well. I was trying to learn Spanish, and just learning to not try to translate things literally, when a friend used “tengo” (“I have/possess”) to mean “I have” as in “I need”, eg. “Tengo ir” (“I have to go”, to pull an example out of my dictionary. I haven’t kept up with my studies, and I don’t remember exactly what she said.) I was very surprised that Spanish speaking people also use the word for “to possess” to mean “to need”.
Any other languages?
**The Oxford English Dictionary on “have to” construction **
b. Hence to have to do: see DO v. 33c, d.
c. With infinitive: To be under obligation, to be obliged; to be necessitated to do something. It forms a kind of Future of obligation or duty.
[Cf. the Future tense of the Romanic langs, e.g. je parler-ai, je finir-ai, I have to speak, to finish.]
1579 FENTON Guicciard. (1618) 6 He told him, he had not to beleeue, that the couetousnesse of Virginio…had moued Ferdinand. 1594 HOOKER Eccl. Pol. I. i. §1 We have…to strive with a number of heavy prejudices. 1596 SPENSER State Irel. Wks. (Globe) 657/2 This is the manner of the Spanyardes captaynes, whoe never hath to meddle with his souldiours paye. 1765 H. WALPOLE Otranto v. (1798) 80 Having to talk with him on urgent affairs. 1831 F. TROLLOPE Dom. Manners Amer. (1894) II. 271 But ‘we had to do it’ as the Americans say. 1848 MRS. GASKELL Mary Barton ix, Mary had to change some clothes after her walk home. 1883 Manch. Exam. 29 Oct. 5/4 In 1831 the firm had to suspend payment. 1892 LOPES in Law Times Rep. LXVII. 144/1, I regret to have to say that I do not believe that evidence. Mod. I have to go to London to-morrow.
**
On -S ending, as in “must needs”:**
forming adverbs, was originally -es, identical with the suffix of the genitive singular of many neuter and masculine ns. and adjs. Several of the adverbs in -es that existed in OE. are genitives either of ns. (neut. or masc.) as dæes by day, nédes NEEDS, ances voluntarily, or of neuter adjs., as sóes truly; on the analogy of these, -es was added, with adv.-forming function, to feminine nouns, as in nihtes by night, endebyrdes in order. OE. had also advs. compounded of tó prep. and a genitive governed by it, as tó-enes (see TO-GAINS), tó-middes (see TO-MIDS); side by side with these there existed parallel and synonymous advs. like on-en AGAIN, on-middan AMID, in which the dat. or accus. was governed by a prep. Hence there arose in early ME. mixed forms such as aeines, amiddes; and the frequent coexistence of the two forms of the same adv., one with and the other without s, led to the addition of s to many advs. as a sign of their function. In some instances the extended form prevailed, as in eftsoons; in others it survived only in dialects, as in oftens, gaylies (Sc.). See also the articles -LING2, -LI(N)GS, -WARD, -WARDS, -WAY, -WAYS.
In once, twice, thrice, hence, since, etc., the suffix is written differently. In AGAINST, ALONGST, AMONGST, AMIDST, and the dialectal onst (see ONCE), the original -es, -s has become -st.
(Note to mods: I realize that the wholesale offering of such posts would be an abuse of my privilege to access the OED online, and promise not to set myself as an etymological guru on the strength of it. But I don’t see the harm in answering an occasional question of this type).