Final answer:
Descartes used dreaming as an example to show that senses can be deceptive, leading to his conclusion that while our perceptions can be doubted, the act of thinking itself confirms our existence.
Step-by-step explanation:
Descartes points to dreaming as evidence that he might be wrong in how he pictures his body. He argued that because dreams can often incorporate experiences we have in real life, it is impossible to distinguish between dreaming and waking life. Through this, he illustrates how our senses can deceive us, and thus, they cannot always be trusted for absolute certainty.
This skepticism led to his famous conclusion: "I think therefore I am," which means that while our perceptions might be deceiving, the fact that we can think is undeniable proof of our existence.