 The legitimacy of the underlying condemnation of Copernicus on theological and rational grounds is even more problematic. Galileo had addressed this problem in 1615, when he wrote his Letter to Castelli and then the Letter to the Grand Duchess Christina. In these texts, Galileo argues that there are two truths: one derived from Scripture, the other from the created natural world. Since both are expressions of the divine will, they cannot contradict one another. However, Scripture and Creation both require interpretation in order to glean the truths they contain—Scripture because it is a historical document written for common people, and thus accommodated to their understanding so as to lead them towards true religion; Creation because the divine act must be distilled from sense experience through scientific enquiry. While the truths are necessarily compatible, biblical and natural interpretations can go awry, and are subject to correction.