The theories of identity over time and causation that I have presented earlier have for the most part been conventional. That is to say that causation and identity are treated by the theories simply as abstractions, which are defined in a completely conventional way, without any physical basis.
At this point you may think that I have gone mad, for clearly there are events in the world that provide a basis for causation. This is not quite what I meant however, it is perhaps more accurate to say that while a definition of causation or identity necessarily contains some appeal to the state of the world (for example in order to say which events are causes of some other event and which events are not) there is nothing in the external world that forces us to pick one definition of causation or identity over another. There are neither causation particles nor identity fields that we can observe. As Hume correctly stated we never observe causation itself, merely sequences of events from which we infer causation.
Of course not every definition of causation or identity is equally good. However if we can’t choose one definition over another based on physical evidence then how can be make a distinction between good definitions and bad ones? Well since the definitions are all equally valid (assuming they are consistent that is), it seems to make sense to pick the definition that agrees most with our common use of the word. This is why I have called my accounts of identity and causation conventional, because the definition given aims to agree with our pre-analytic usage of causation and identity as much as possible.
This however supposes that somehow we already have notions of causation and identity. If it is true that there is no objectively real thing that is causation or identity over time in the world then where do these notions come from? It seems to me that they arise as natural abstractions that simplify our dealings with the world. For example life would be much more complicated if every time you left the room you weren’t sure that the table you found when you came back was the same one that you had left earlier. Our observations that the objects we find around us seem to be similar to objects that we had observed in the past (with differences being relatively predictable and being greater the more time has gone by) naturally leads to the idea that these objects are somehow the same as the objects we have observed in the past. This idea greatly simplifies our lives, and for the most part serves us well; it is rare that one thing is replaced with something very much like it without us being aware of it. Likewise the idea of causation naturally arises from a common sense understanding of how the world works. For example imagine a person who has lived in a box all of their lives suddenly being exposed to a mill powered by a water wheel. If asked what the cause of the water wheel turning is they will have no idea. However if you show them the mill stopped when the river has run dry it will become apparent to them that somehow the river is necessary for the turning of the water wheel, and from this idea the notion of a cause is formed. Like the notion of identity, our intuitive understanding of causation is a mental shorthand for what would otherwise be a complicated thought process. Describing something as a cause is to understand how events progress under different circumstances, as well as to know how the event we have labeled as a cause contributes to that progression. Once we have mastered the idea of causation we can use this complicated system of thought in our day-to-day lives without having waste time thinking about it every time we wish to describe events.
Of course I have been presenting these notions as if they are learned in an individual’s lifetime. Although it is possible that this is how we acquire them it is more likely that they have been hardwired into our minds as a result of evolution. Our ancestors who were born with the ability to abstract various complications away into the simpler ideas of identity and causation (as well as numerous other abstractions too I suppose) probably had a natural advantage over their rivals who could not. If this is true then one way of looking at ideas such as causation and identity is that they are a-priori (they are available to us in the absence of experience). They have many properties in common with other ideas that have been considered for the status of a-priori, for example they can neither be confirmed nor refuted by experimental evidence. However even if they are a-priori it does not give these abstractions some special status or connection to the truth. It is perfectly reasonable that our intuitive notions of causation or identity may be contradictory or simply ill-defined. This is why philosophers develop more formal definitions. Although ultimately it is our intuitive notions that are the standard for their success, the definitions devised for these concepts also strive to be consistent and concrete where are intuitive notions are lacking in this respect.
You may now be wondering how these abstractions can be of any use to us at all. Since they are based on intuitive notions and held to no higher standard than consistency how can they possibly tell us anything new? Well by themselves they can’t. I admit that no matter how much we like a particular definition of causation or identity there is nothing that the definition can tell us that we didn’t already know. Their use then is not as the basis for further theories, but as a way of simplifying complicated concepts as part of the argument for or against another theory. For example, if I propose a theory of information in which causation is necessary for the transmission of information, then I can appeal to a definition of causation to clarify what I mean. In this way then these definitions can contribute to a philosophical discourse that is about objectively true statements, and not matters of convention, by clarifying and making precise ideas that may be otherwise understood differently by different people. Although this may seem like a minor contribution abstraction can be a powerful tool, and preciseness and clarity are what separate good philosophy from bad.