Meditation IV deals almost entirely with the nature and origin of truth and error. Descartes asserts that knowledge of God will lead us to knowledge of other things. Because God is perfect, it is impossible that God would deceive Descartes, because deception is an imperfection. But Descartes knows himself to be capable of error, and so he has to examine the nature of his own ability to err. He concludes that God must have created him so that he could be wrong. Imperfect things, like him, may occupy their place in the world perfectly. In other words, Descartes’ imperfections may be what make him perfect for his role in God’s plan. He further reasons that his own propensity to err must be his own failure to use his method to approach the knowledge sent to him by God.
Descartes decides in meditation V to begin to examine whether he can believe in the material world by examining the essence of material things in relation to God. He looks at his own ideas about the material world and separates them into two categories: distinct and confused. Mathematical ideas are distinct and therefore exist. He further concludes that no truth, no science, and no certitude can exist without the knowledge of the existence of God. He realizes that the existence of everything depends on God and reasons on that basis that he doesn’t have to doubt everything anymore. Descartes knows that God has given him the capacity to learn the truth about both intellectual and corporeal things.
Meditation VI is devoted to investigating whether material things exist. Finally, Descartes finds that it seems safe to believe that his God-given senses convey the truth to him. Above all, his senses convey to him that he has a body. He maintains that, though there is some mysterious link by which the mind is joined to the body, the mind and body are different things, and the mind will outlive the body. Having decided this, Descartes dismisses all his doubts of the past and determines, at last, that he can trust his senses.
In the first introduction, to the theologians of the Sorbonne, Descartes takes pains to avoid charges of heresy. He had already seen, in the case of Galileo, what could happen if the church disapproved of scholarly work. Although Descartes ultimately comes to conclusions that would be acceptable to the theologians—God exists; the human soul is eternal—it might have been considered heretical to feel that it was even necessary to logically prove God’s existence. The Catholic Church, after all, considers God’s existence to be a matter of fundamental, unquestionable truth. The introduction to the reader reiterates his intention of publishing for an audience of logically thinking but uneducated readers.
One way in which Descartes tried to make his work acceptable to a conservative Catholic audience was to structure the meditations in a form similar to that of the Spiritual Exercises of St. Ignatius of Loyola, the founder of the Jesuit Order. The Spiritual Exercises recommends a six-step path in which the Christian begins by releasing all attachment to the material world, but after gaining confidence in God, the Christian returns to the material world with a renewed sense of purpose. Descartes’ purpose was radically different, but the Meditations follow a sixfold structure that is, on the surface, similar. The first meditation proves that all things are subject to doubt. The second asserts that if we doubt, there must be a mind to do the doubting. The third meditation concerns Descartes’ proof of the existence of God. In the fourth, he explains how to distinguish what is true from what is false. In the fifth, he explains corporeal nature and further proves the existence of God. In the sixth, Descartes explains the difference between understanding and imagination and proves that the human mind is distinct from the body. As with the Spiritual Exercises, the steps go from detachment from the material world to establishing confidence in God to the achievement of confidence in the existence of the material world.
The three arguments that Descartes uses to make us doubt our own knowledge—the Dream argument, the Deceiving God argument, and the Evil Demon argument—are not meant to be taken literally. To prove anything beyond a shadow of a doubt, Descartes has to call everything into doubt. This strain of thinking in philosophy is called skepticism, the practice of critically examining one’s own knowledge and perception to determine whether they are true. But skeptics also have to ask whether there is such a thing as true knowledge—in other words, whether it is possible to know anything for certain. Descartes was not the first person to employ skepticism—the tradition reaches back as far as the history of philosophy.