Should

• POS: Verb (usu participle)

CIDE DICTIONARY

Should, imp. [OE. sholde, shulde, scholde, schulde, AS. scolde, sceolde. See Shall.].

 Used as an auxiliary verb, to express a conditional or contingent act or state, or as a supposition of an actual fact; also, to express moral obligation (see Shall); e. g.: they should have come last week; if I should go; I should think you could go.  Shak.  [1913 Webster]

Syn. -- See Ought.

OXFORD DICTIONARY

Should, v.aux. (3rd sing. should) past of SHALL, used esp.:
1 in reported speech, esp. with the reported element in the 1st person (I said I should be home by evening).

Usage

Cf. WILL(1), WOULD, now more common in this sense, esp. to avoid implications of sense 2.
2 a to express a duty, obligation, or likelihood; = OUGHT(1) (I should tell you; you should have been more careful; they should have arrived by now). b (in the 1st person) to express a tentative suggestion (I should like to say something).
3 a expressing the conditional mood in the 1st person (cf. WOULD) (I should have been killed if I had gone). b forming a conditional protasis or indefinite clause (if you should see him; should they arrive, tell them where to go).
4 expressing purpose = MAY, MIGHT(1) (in order that we should not worry).

THESAURUS

Should

be expedient, be forced, be in for, be necessary, be obliged, cannot do otherwise, cannot help but, had best, had better, have got to, have need to, have to, must, need, need to, needs must, ought, ought to