What is "should'st"

Usage examples of "should'st".

She straight began: "When my desire invited thee to love The good, which sets a bound to our aspirings, What bar of thwarting foss or linked chain Did meet thee, that thou so should'st quit the hope Of further progress, or what bait of ease Or promise of allurement led thee on Elsewhere, that thou elsewhere should'st rather wait?

And anon there appeared the Sangreal unto the white knights, but thou was so feeble of good belief and faith that thou mightest not abide it for all the teaching of the good man, but anon thou turnest to the sinners, and that caused thy misadventure that thou should'st know good from evil and vain glory of the world, the which is not worth a pear.