Earliest Yiddish (בראשית-ייִדיש): -1250
- Entirely in Ashkenaz I
- Entrance of the Hebrew-Aramaic, Romance and German components into the fusion
Old Yiddish (אַלטייִדיש): 1250-1500
- Transition from Ashkenaz I to Ashkenaz II
- Entrance of the Slavic component into the fusion
Middle Yiddish (מיטל-ייִדיש): 1500-1700
- Equilibrium of Ashkenaz I and Ashkenaz II
- Demarcation of Western vs. Eastern Yiddish
Modern Yiddish (נײַ-ייִדיש): 1700-
- Great preponderance of Ashkenaz II
- Shrinking of Western Yiddish and expantion of Eastern Yiddish into high secular social functions
* Ashkenaz I = German-speaking lands
** Ashkenaz II = Slavic-speaking lands
Yiddish as a Fusion Language
- Source languages: Hebrew-Aramaic ("לשון-קודש"), Romance, German, Slavic (mainly Polish, Ukrainian, Belorussian, and later Russian)
- Determinants: those parts of the source languages that could theoretically enter Yiddish
- Components: those parts of the determinants that actually entered Yiddish