beyoudaoicibaDictYouDict[be 词源字典]
be: [OE] There are four distinct components that go to make up the modern English verb be. The infinitive form be comes ultimately from an Indo-European base *bheu-, *bhu-, which also produced, by other routes, future and physical. Its Germanic descendant was *bu-, which signified on the one hand ‘dwell’ (from which we get booth, bower, byre, build, burly, byelaw, and the final element of neighbour), and on the other hand ‘grow, become’, which led to its adoption as part of the verb expressing ‘being’ (in Old English particularly with the future sense of ‘coming to be’). Am and is go back to the ancient Indo- European verb ‘be’, *es- or *s-, which has contributed massively to ‘be’ verbs throughout all Indo-European languages (third person present singulars Greek esti, Latin est, French est, German ist, Sanskrit ásti, Welsh ys, for example) The Indo-European first and third person singular forms were, respectively, ésmi and ésti.

For the present plural Old English used the related sind(on) (as found in Latin sunt, French sont, and German sind), but this died out in the 12th century, to be replaced by are, which comes from a Germanic base *ar- of unknown origin. From the same source is the now archaic second person singular art. The past tense forms was, were come ultimately from an Indo-European base *weswhich meant ‘dwell, remain’.

Related words in other Indo-European languages include Sanskrit vásati ‘dwell, remain’ and Gothic wisan ‘remain, continue’.
=> booth, bower, build, burly, byelaw, byre[be etymology, be origin, 英语词源]
be (v.)youdaoicibaDictYouDict
Old English beon, beom, bion "be, exist, come to be, become, happen," from Proto-Germanic *biju- "I am, I will be." This "b-root" is from PIE root *bheue- "to be, exist, grow, come into being," and in addition to the words in English it yielded German present first and second person singular (bin, bist, from Old High German bim "I am," bist "thou art"), Latin perfective tenses of esse (fui "I was," etc.), Old Church Slavonic byti "be," Greek phu- "become," Old Irish bi'u "I am," Lithuanian bu'ti "to be," Russian byt' "to be," etc. It also is behind Sanskrit bhavah "becoming," bhavati "becomes, happens," bhumih "earth, world."

The modern verb to be in its entirety represents the merger of two once-distinct verbs, the "b-root" represented by be and the am/was verb, which was itself a conglomerate. Roger Lass ("Old English") describes the verb as "a collection of semantically related paradigm fragments," while Weekley calls it "an accidental conglomeration from the different Old English dial[ect]s." It is the most irregular verb in Modern English and the most common. Collective in all Germanic languages, it has eight different forms in Modern English:

BE (infinitive, subjunctive, imperative)
AM (present 1st person singular)
ARE (present 2nd person singular and all plural)
IS (present 3rd person singular)
WAS (past 1st and 3rd persons singular)
WERE (past 2nd person singular, all plural; subjunctive)
BEING (progressive & present participle; gerund)
BEEN (perfect participle).

The paradigm in Old English was:

SING.PL.
1st pres.ic eom
ic beo		we sind(on)
we beoð
2nd pres.þu eart
þu bist		ge sind(on)
ge beoð
3rd pres.he is
he bið		hie sind(on)
hie beoð
1st pret.ic wæswe wæron
2nd pret.þu wærege waeron
3rd pret.heo wæshie wæron
1st pret. subj.ic wærewe wæren
2nd pret. subj.þu wærege wæren
3rd pret. subj.Egcferð wærehie wæren


The "b-root" had no past tense in Old English, but often served as future tense of am/was. In 13c. it took the place of the infinitive, participle and imperative forms of am/was. Later its plural forms (we beth, ye ben, they be) became standard in Middle English and it made inroads into the singular (I be, thou beest, he beth), but forms of are claimed this turf in the 1500s and replaced be in the plural. For the origin and evolution of the am/was branches of this tangle, see am and was.
That but this blow Might be the be all, and the end all. ["Macbeth" I.vii.5]