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."