working out its internal angles. P2. Imagining takes more effort than understanding. C1. Therefore, imagination and understanding are different. P3. Imagination is not essential to me, while understanding is. I cannot be me (a thinking thing) without understanding, but I can be me without imagination. P4. The best explanation for all these differences is that imagination depends upon having a body. (Imagination draws its ideas from the body, which makes its ideas sensory images and difficult to work with, and makes imagination not essential to a thinking thing. Being purely mental, understanding draws its ideas from itself, making them non-imagistic and easy to work with, and understanding is essential to a thinking thing.) C2. Therefore, it is probable that the body (a physical object) exists. It is, however, only probable, so the argument doesn’t give us knowledge of the existence of physical objects. Descartes’ second argument is from perception (p. 28). It is natural to think that we know that physical objects exist because we perceive them. Our perceptions are both involuntary and more lively and vivid’ than imagination or ‘much memory. One explanation is that they are caused by physical objects that exist independent of our minds. But Descartes reminds us of his arguments from perceptual illusion and dreaming (p. 29). The mere fact that perceptual experiences are vivid and involuntary isn’t enough to show that they are caused by mind-independent physical objects. It does, however, provide the starting point for his next argument (p. 30). I have added in missing premises in brackets, some of which Descartes assumes because he has argued for them previously.
working out its internal angles. P2. Imagining takes more effort than understanding. C1. Therefore, imagination and understanding are different. P3. Imagination is not essential to me, while understanding is. I cannot be me (a thinking thing) without understanding, but I can be me without imagination. P4. The best explanation for all these differences is that imagination depends upon having a body. (Imagination draws its ideas from the body, which makes its ideas sensory images and difficult to work with, and makes imagination not essential to a thinking thing. Being purely mental, understanding draws its ideas from itself, making them non-imagistic and easy to work with, and understanding is essential to a thinking thing.) C2. Therefore, it is probable that the body (a physical object) exists. It is, however, only probable, so the argument doesn’t give us knowledge of the existence of physical objects. Descartes’ second argument is from perception (p. 28). It is natural to think that we know that physical objects exist because we perceive them. Our perceptions are both involuntary and ‘much more lively and vivid’ than imagination or memory. One explanation is that they are caused by physical objects that exist independent of our minds. But Descartes reminds us of his arguments from perceptual illusion and dreaming (p. 29). The mere fact that perceptual experiences are vivid and involuntary isn’t enough to show that they are caused by mind-independent physical objects. It does, however, provide the starting point for his next argument (p. 30). I have added in missing premises in brackets, some of which Descartes assumes because he has argued for them previously.