The Inverse Square Law (ISL) of Universal Gravitation is the epitome of the great achievement of mathematical natural philosophy. But what exactly was this achievement? Newton and his followers presented it as the discovery of the simple, perfect laws underlying all seemingly-unruly phenomena. For Kepler, the first to introduce the ISL into natural philosophy (as the law of the decline of light with distance), mathematics was indeed the human means to decipher God’s perfect harmonies, but through the seventeenth century this belief gradually eroded. For Newton, the ISL became a tool of approximation, rooted in, and gaining its authority from, human practice: the mathematization of nature required relinquishing the certainty and perfection that mathematical knowledge was expected to provide.