They say every explanation demands its own explanation, and that such recursion leads to an infinite regress of explanations, or “turtles” going “all the way down”. But just as in physics—where reference frames are arbitrary until one is chosen—or in math—where axioms are taken as given truths, we can always select something useful as a foundation. No matter how arbitrary it might otherwise seem, that choice becomes the bottom upon which everything else is built. This blog is where I write about turtles, especially those at the bottom.