It's an interesting question as to how far we can comfortably or meaningfully take counterfactuals. At some level it is completely mundane to say things like, if I had taken a different route to work today, I wouldn't have gotten caught in that traffic jam. We aren't thrown into a maelstrom of existential confusion as we struggle to understand what it could mean to have different memories than those we do. How could I have not gotten into that traffic jam? What would happen to those memories? Would I still be the same person? We deal with these kinds of counterfactuals all the time. They are one of our main tools for understanding the world and learning which strategies work and which don't.
Then there are much more extreme counterfactuals. Apple Computer head Steve Jobs gave a pretty good graduation speech at Stanford last week, http://news-service.stanford.edu/news/2005/june15/jobs-061505.html. He explains that he was adopted, and his life was changed in a major way by the circumstances. His biological mother, an unwed grad student, wanted him raised by college graduates, so he was set to be adopted by a lawyer and his wife. At the last minute the lawyer decided he wanted a girl, so Jobs ended up being given to a blue collar couple, neither of whom had gone to college. They were good parents and treated him well, sacrificing so he could go to college, but after six months Jobs dropped out, seeing little value to consuming his family's entire savings. He continued to attend classes on the sly, got into computers and the rest is history. But imagine how different his life would have been if the original plan had gone through and he had been adopted by a successful lawyer, perhaps raised in an upper class household with his every wish met. He would have gone to an Ivy League college and probably done well. But it would have been a totally different life path. Does it make sense for Jobs to say, who would I have been if that had happened? Or would he have been such a totally different person that this stretches the idea of a counterfactual beyond reason? I think his telling the story demonstrates that he does think this way sometimes. Yet none of the memories or experiences that he has would have been present in this other version. At most the two versions might have shared some personality traits, but even those are often strongly influenced by upbringing - his tenacity in the face of adversity, for example, might never have become so strong in a life where everything came easily. Probably there are many people in the world who are at least as similar to Steve Jobs in personality as the person he would have been if his early life had gone that other way. The point is that we can imagine a range of counterfactuals where the difference is a matter of degree, not kind, from trivial matters all the way up to situations where we would have to consider ourselves a different person. There is no bright line to draw that I can see. So yes, if you can imagine what it would have been like to eat something else for breakfast, then you should be able to imagine what it would have been like to be born as someone else. It's the same basic technique, just applied to a greater degree. Hal Finney
