If I’m not wrong, the verb conjugation in the past used to be:
I have we have thou hast ye have he/she/it hath they have
This conjugation is closer to its equivalent in the German language:
ich habe wir haben du hast ihr habt er/sie/es hat sie/Sie haben
The thing is: Every verb in every tense in German ends with -st in the second person singular, and as far as I know, in Elizabethan English the verbs used to end in this way as well in the second person singular (thou shouldst, canst, makest, eatest, composest, etc.).
Why exactly did the old thou disappear, as well as related forms thy, thee, thyself, and thine, as well as the corresponding verb ending -st? Same for -eth in third person singular (it hath, maketh, etc.), why did it just disappear from daily usage?
I’m a Brazilian and my mother-tongue is Portuguese, so I’m not well aware of the background of this, and I am very curious. These forms can be found in the old King James Bible and in the poetry of William Shakespeare, as well as in many other sources, but I would like to know exactly why they’re gone, and for what reasons.