Rationalism and empiricism are two different ways of thinking about how we learn and know things in philosophy. When we look at the ideas of Descartes, we can see that he had a strong belief in rationalism, which is very different from empiricism.

Rationalism says that the main way we gain knowledge is through our mind and reasoning, not just what we see or feel. Descartes famously said, "Cogito, ergo sum," which means "I think, therefore I am." This idea shows that just by thinking, we can be sure that we exist. For Descartes, it’s important to realize that some ideas are already in our minds, and we can find truths by using logic and reasoning alone.

On the other hand, empiricism teaches that we learn mainly through our senses. Empiricists believe that what we see, touch, hear, taste, and smell helps shape our understanding of the world. They say that without these senses, we can't really know what is true.

Descartes also had doubts about how trustworthy our senses are. He pointed out that our senses can be fooled. For example, things like optical illusions or dreams can trick us. So, while empiricists rely on what they can sense, Descartes believed that using our reason was a more reliable way to find knowledge.

In summary, the big difference between rationalism and empiricism involves where we get our knowledge. Rationalism values ideas we already have and logical thinking, while empiricism believes in learning through observation and experiences. Descartes' exploration of doubt leads him to show that using reason is the best way to reach true understanding.