Why we need formal ontologies

 Consider the sentence I wish I had been born earlier. This implies that we are considering possibilities in which the same individual $A$ had a different life-history in a different possible world. By life-history we mean the total sequence of states, actions and events involving $A$ (all a part of a world $W$) during a certain time interval L from the time of birth to the time of death. 

 For a world $W$ can the life-history of an individual $A$ be deduced or defined ? Or is the identity of an individual $I$ fixed  a priori ? Why do two life-histories corresponding to two different worlds correspond to the same individual ? And even for the actual world how could we interpret prexistence or reincarnation or survival in some different form all in the same time-line of the actual world ? What is that which guarantees the identity and continuity of such different embodiments ? 

 Let each world $W$ is endowed with a partition according  to world-time $T$ (of which the $L$ of an individual is a subinterval). Thus we speak of the world $W_t$ at time $t$. The relationship between possible worlds will reflect a branching structure for $T$.  Given a possible world $W$ and time $t\in T$, we can consider a set of possible worlds $W_1^t,...W_n^t$ which coincide with $W$ up to $t$ and then begin to differ.  

This same construction carries over to life-histories of individuals.  It gives reasonable sense to sentences of the type I wish I had not made that decision. Of even statements of an individual $I_1$ regarding an individual $I_2$: if $I_2$ hadn't died young he might have become famous.  This is expressed by the branching structure on possible life-histories in possible worlds which coincide up to a time $t$.

But there is a great asymmetry involved in If he had been born earlier he would have been able to have met Bertrand Russell. Without a previous theory of individuation and identity we are forced to conclude that such an expression is meaningless.  But a theory of individuation and identity means some kind of more or less sophisticated formal ontology and even a  'general systems theory'. We consider the idea of a 'rigid designator' and thought experiments such as the 'twin earth'  problematic.

Mereology is also connected to such a formal ontology. Here are some older notes and sketches illustrating what a formal ontology or general systems theory might look like.