case syncretisms

[aldai]

Well. The existance of syncretism is not my problem at all. Actually that
is what we are looking for. The problem is: syncretism between what?:
For instance:
Genitive and Partitive
Genitive and Ablative
Ablative and Perlative
Genitive and Passive agent
Passive agent and Ergative??
Genitive and Source
Genitive and Future????
Genitive and Purpose??????
Source and Cause
Cause and Goal, Allative, Benefactive, Purpose, Dative

It seems possible to find syncretism between cases meaning Goal and
Source and Perlative. Spanish "por" might be such a case. Although the
intermidiate state of Cause might be necessary. I don't know. (Heine,
Claudi & Hunnemeyer 1991: 162).

My problem is how to order cronologically all these steps.