Where does “ては” come from?

ては (Japanese) comes from Japanese と言えば, from Japanese と, from Old Japanese と, from Proto-Japonic tə, from Proto-Uralic tä — that.

ては (Japanese): "undesirable assumption": if; "indicates a reason...

Definitions

ては traces back through 3 separate lines of ancestry.

Step	Language	Word	Meaning
1	Japanese	と言えば	—
2	Japanese	と	with; and; a particle following a phrase or...
3	Old Japanese	と	—
4	Proto-Japonic	tə	place
5	Proto-Uralic	tä	that

Step	Language	Word	Meaning
1	Japanese	ば	In Modern Japanese, attaches to the kateikei, and...
2	Japanese	は	what about, where is; Inserted between two verbs...
3	Old Japanese	は	—

Step	Language	Word	Meaning
1	Japanese	つ	indicates the completion of an action; indicates...
2	Old Japanese	つ	—