Word Origin & History
O.E. sceal "I owe/he owes, will have to, ought to, must" (infinitive sculan, pt. sceolde), a common Gmc. preterite-present verb, from P.Gmc. *skal-, *skul- (cf. O.S. sculan, O.N., Swed. skola, M.Du. sullen, O.H.G. solan, Ger. sollen, Goth. skulan "to owe, be under obligation;" related via past tense
form to O.E. scyld "guilt," Ger. Schuld "guilt, debt;" also O.N. Skuld, name of one of the Norns). Ground sense probably is "I owe," hence "I ought." The sense shifted in M.E. from a notion of "obligation" to include "futurity." Its past tense form has become should
(q.v.). Cognates outside Gmc. are Lith. skeleti "to be guilty," skilti "to get into debt;" O.Prus. skallisnan "duty," skellants "guilty."