Where does “those've” come from?

those've (English) comes from English those, from Middle English thos, from Middle English tho, from Old English þā, from Proto-Germanic þai, from Proto-Indo-European to-, from Proto-Indo-European só — this; that.

Ancestry of “those've”, step by step

those've traces back through two separate lines of ancestry.

via English those

StepLanguageWordMeaning
1Englishthoseplural of that
2Middle Englishthosthose
3Middle Englishthothe
4Old Englishþāthe, those; then, when; those
5Proto-Germanicþaithey; those; nominative plural masculine of *sa
6Proto-Indo-Europeanto-it; that; the, that
7Proto-Indo-Europeanthis; that

via English ’ve

StepLanguageWordMeaning
1English’vein its sense marking the perfect or retrospective aspect
Every word from Proto-Indo-European