Savage -Kinds of Necessity Assumptions Synchronic and diachronic possibility are logically independent; time is branching; I am 38 years old Definitions Diachronic possibility = what is possible for an object to become going forward from its actual point on its timeline. Synchronic possibility = what is possible for an object now given the current moment and at all past current moments on its current timeline. Degrees of possibility Temporal possibility Nomic Metaphysical Logical Diachronic I could be somewhere other than where I am. ~ I could be biologically 37 years old. ~ I could be an expert on quantum mechanics. ~ I could be immortal. ~ I could grow wings. ~ I could be made of ice. ~ I could be biologically ageless I could be an expert on quantum mechanics. I could be somewhere other than where I am. I could be immortal. I could grow wings. ~ I could be biologically 37 years old. * I could be made of ice. ~ I could be biologically ageless I could be immortal. I could be biologically 37 years old (supposing I started to age in reverse). I could be an expert on quantum mechanics (supposing I'm immortal). I could grow wings (supposing the world changes and we evolve to cope). I could be made of ice. I could be somewhere other than where I am. ~ I could be biologically ageless Synchronic I could be biologically 37 years old (because there is at time at which I was conceived slightly earlier than I actually was). ~ I could be somewhere other than where I am. I could be an expert on quantum mechanics. ~ I could be immortal. ~ I could grow wings. ~ I could be made of ice. ~ I could be biologically ageless. I could grow wings. I could be biologically 37 years old. I could be an expert on quantum mechanics. ~ I could be made of ice. ~ I could be somewhere other than where I am. I could be immortal. ~ I could be ageless. I could be made of ice. I could be immortal. I could be 37 years old. I could be an expert on quantum mechanics. I could grow wings. ~ I could be somewhere other than where I am (supposing it is a contradiction to be in two places at once, and I am some place). ~ I could be biologically ageless Entailment relations of note Synchronic logical possibility --> diachronic logical possibility Diachronic logical possibility -/-> synchronic logical possibility Potential problems First, if I could be infinitely old, that seems synchronically logically possible, but not diachronically logically possible. If this is correct, then the above entailment is false. My intuition, however, is to interpret being infinitely old as equivalent to the claim of being biologically ageless, and this plausibly is neither synchronically nor diachronically logically possible. Second, if we count age as going forward in time on any time line, and if we count the possibility of getting younger as involving going objectively backwards in time, then given the definition of diachronic possibility, logically, I could not be 37 years old. Alternatively, if we allow for time travel, and we count personal time as age determinative, then I still could not possibly be 37 years old since I would still be getting older traveling back to an earlier time. If correct, then once again, the above entailment is false. However, I claim that getting older is not simply to be in existence for a certain period of time. Rather, to age is to undergo some kind of biological or physical process of decaying change over time. If then we were to find the fountain of youth, it would be diachronically logically possible for me to be 37 years old. And at any rate, even if the previous issues are fundamentally problems, all they really show is that diachronic and synchronic logical necessities are even more independent than we might have originally thought.1 1 Thanks to Bernard Molyneux, Chris Tillman, David Sanson, and Paul Pietroksi for discussion.