古英语中“thou hast”“thou doth”以及在动词后加“est”的用法解释?

古英语和现代英语中的第二人称代词对应如下：
古英语:thou,thee,thy,thine,thyself
现代：you（主语）,you(宾语）,your ,yours,yourself
thou hast = you have
thou dost = you do
在“thou"后面出现的动词在古英语中通常以“-st"或“-est"结尾,现在时和过去时都是这样.至于原因我想是约定俗成的用法.常用动词举例：
to be:thou art (thou'rt),thou wast
to do:thou dost,thou didst
to go:thou goest,thou wentest
to have:thou hast,thou hadst
to know:thou knowest,thou knewest
to drive:thou drivest,thou drovest
to make:thou makest,thou madest
to love:thou lovest,thou lovedest
to pull:thou pullest,thou pulldest
to write:thou writest,thou wrotest
to turn:thou turnest,thou turnedst
to return:thou returnest,thou returnedst
to wear:thou wearst,thou worest
may:thou mayst,thou myghte
shall:thou shalt,thou shouldst
will:thou wilt