 In many familiar cases, our past experience is a good guide to when an apparent coincidence calls for further explanation. As Hume emphasized, however, intuitive assessments from everyday life of whether a given event is likely, or requires a further explanation, do not extend to cosmology. Recent formulations of fine-tuning arguments often introduce probabilistic considerations. The constants are “fine-tuned”, meaning that the observed values are “improbable” in some sense. Introducing a well-defined probability over the constants would provide a response to Hume: rather than extrapolating our intuitions, we would be drawing on the formal machinery of our physical theories to identify fine-tuning. Promising though this line of argument may be, there is not an obvious way to define physical probabilities over the values of different constants, or over other features of the laws. There is nothing like the structure used to justify physical probabilities in other contexts, such as equilibrium statistical  mechanics.[50] 