Visions Like Paintings
"Still, it has to be admitted that the visions that come in sleep are like paintings: they must have been made as copies of real things; so at least these general kinds of things— eyes, head, hands and the body as a whole—must be real and not imaginary." (First Meditation)
In this Meditation, Descartes is examining the world and its elements, trying to determine which elements he should doubt and which he should trust. Ultimately he can only be positively certain that his own mind exists, but he convinces himself that he isn't dreaming, or at least the things he sees in his dream must also exist in the waking realm: even things in dreams are based on real objects. The following question, however, is whether these external objects have any existence in themselves; that question is for a later time.
The Blissful Prisoner
"Like a prisoner who dreams that he is free, starts to suspect that it is merely a dream, and wants to go on dreaming rather than waking up, so I am content to slide back into my old opinions." (First Meditation)
Near the end of the First Meditation, Descartes describes the difficulty of his undertaking to discover the true nature of reality; not only is it intellectually challenging, but it's emotionally challenging as well: discovering that life itself is a lie will destroy the most stable of minds. He describes the sensation of not wanting to discover the truth, instead choosing to remain blissfully ignorant. His drive for truth, however, would never allow such irresponsibility.
A Deep Whirlpool
"I feel like someone who is suddenly dropped into a deep whirlpool that tumbles him around so that he can neither stand on the bottom nor swim to the top." (Second Meditation)
Having just completed his systematic destruction of reality, Descartes finds himself stumbling around in the dark, relying on only the existence of his mind to ground him in life. The sensation of losing one's grounding in reality is philosophically disorienting, much in the same way as a man tumbling about in a whirlpool from which it seems there is no escape.
A Horse with Wings
"The influence runs the opposite way: the necessity of the thing constrains how I can think, depriving me of the freedom to think of God without existence (that is, a supremely perfect being without a supreme perfection), like my freedom to imagine a horse with or without wings." (Fifth Meditation)
Descartes has just explained his way of seeing God: His existence is necessarily and completely inextricable from that of reality itself, and Descartes cannot even fathom one without the other. This type of necessary association is a stark contrast to the idea of separable yet coexistent objects, like a horse with wings. He can imagine a horse without wings, but he cannot imagine reality without God.
A Damaged Ship
"If this were not so, I wouldn’t feel pain when the body was hurt but would perceive the damage in an intellectual way, like a sailor seeing that his ship needs repairs." (Sixth Meditation)
In the final chapter of the Meditations, Descartes uses this simile to explain the relationship between the mind and the body. He believes that they are two entirely separate, distinct substances, but God lodged the mind inside the body for some reason, so he must attempt to reconcile this seeming discrepancy. To do so, he comes up with this relationship: the body is essentially a vehicle for the mind to get around in and communicate with other minds, like a ship carrying a sailor to and fro. He immediately rejects this theory, however, because the body's injury causes pain in the mind, implying that their connection is far stronger than he might be tempted to think.
