I believe, Most Illustrious and Serene Lady, that Holy Scripture and nature proceed equally from the divine Word: the former, under the inspiration of the Holy Spirit; the latter, as the most faithful observer of His orders and commandments. Scripture, in order to be understood in many places, and to teach the human mind truths it could not discover by itself, is necessary; but nature is a book always open before our eyes, of universal reading, and which never shows anything other than what it is. It is therefore reasonable to think that nature acts according to the same laws that Scripture presents to us, and that these two writings concur perfectly in all that is essential. Indeed, God, through nature, acts just as we see Him act in Scripture: He does not press men to abandon the use of their own faculties when those faculties suffice, but He grants supernatural assistance to needs that exceed the common. He does not give, at every moment, miracles to guide our steps and our eyes, when experience and the senses may suffice; nor does He intend that, when we can draw from sensible things and necessary demonstrations a full certainty, we should doubt what Scripture seems at first glance to say about those same things. For I maintain that, in questions of natural science which do not directly concern faith, we must begin with observation and the experience of the senses, and not with the authority of texts. It belongs to those who make and attentively consider such observations to interpret those passages that appear contradictory. For one cannot doubt that what is contrary to demonstrated truth must be understood otherwise. Two truths can never contradict one another: the demonstrations of science, which soundly examine the effects of nature, and the inspired word, which cannot err, both drawing their origin from the same source. We must therefore seek, with the utmost care, how to reconcile the one with the other, never granting the preference to the authority of many writers over the demonstrations of sensible things; for nature, offered to us by the supreme Benefactor, shows herself as she is, and never transgresses the terms of the law given to her. Consider: when an astronomer wishes to describe, for the needs of agriculture or navigation, the position of the stars, he does not trouble himself to find where the Earth, the Sun, or the Moon absolutely are, nor how they truly move; it suffices that he suppose the terrestrial globe as immovable at the center, and then, following the rules of his art, he arrives at his conclusions. It is clear, then, that in such cases one speaks not according to the truth of the matter, but according to the understanding of ordinary people, who have in view only practical use. It is the same with Scripture: it accommodated its discourse to the capacity of ordinary men, and did not wish to give occasion to think that men, so limited, were capable of understanding what God, in His infinite wisdom, placed in nature. The Sun, according to the expression of Scripture, rises and sets; the heart beats, light comes into the world; and ordinary people, who are the greatest number, hear, understand, and are satisfied. But let a man of science examine the nature of the Sun, and he will not conclude from the words of Scripture that the Sun moves and the Earth is at rest; for he knows that the language of the holy books, which does not cease to make itself heard by the greatest number, speaks according to the appearance of the senses. And for this reason, so great and so praiseworthy is this conduct of Scripture, accommodating its words to the capacity of the weakest and most ignorant readers, that one cannot help admiring the profound wisdom and divine providence with which it deals with men. The same may be said of nature: it does not begin with first causes and abstract principles, but with what our senses can reach. Moreover, the intention of the Holy Spirit is to teach us how one goes to heaven, and not how heaven goes. This sacred phrase seems to me so apt that it may serve as a rule for all our disputes: what theology teaches about salvation is certain and unchanging; but the curiosity of scholars, guided by experience and reason, extends its dominion over the machine of the world without the faith suffering thereby. Let no one, then, accuse us of daring to reform the sciences by means of the holy books; the sacred monuments, indeed, were not made to instruct us in the sciences, but for the salvation of souls. Let each take, with the grace of God, the path that lies open before him: Scripture to ascend toward heaven, and nature to understand the heaven that goes before us.