 Mersenne did not think that our inability to understand the ultimate cause and intimate nature of things should be an object of lament. The mere knowledge of effects and appearances might be enough for human needs. For one thing, it has enough pragmatic virtue, as it can serve us as a guide in our actions. Besides, as outwards appearances, crust and superficies may be rigorously described, through measurement and mathematics, the sort of knowledge that can be gained here is as perfect and certain as one could wish—although not of the sort dogmatic physicians and metaphysicians are seeking.