It is the mind that is the source of ideas, even those which we are very certain of, and not the senses or the imagination. From our mind, we learn about our bodies and every other material thing in the world. In my opinion, Descartes was right in arguing that the mind is the source of our ideas. Everything else we know, we know because we thought about it and accepted that it exists. We experience many things on a daily basis and what we think of our experiences becomes our idea of the experience. An experience can be a sad one if we think that it is a sad experience. However, the same experience could be just an ordinary experience if we do not think that it is sad. However, we know whether an idea is true or false based on our experiences and the knowledge of other people about it. When we think we hear a baby crying in the next room, we can know...

It could be that it is only the sound of a baby crying from the television or the radio.
Descartes's ideas tell us that thinking about things is important. In learning, people should be skeptical and not merely accept everything that is being taught to them. In the same manner, people should not rely on everything they hear and see, instead, they should think about the truth in it. People should learn how to think and speculate. At the same time, it is also important to use one's senses and experience learning alongside thinking.

References

Descartes, Rene. Meditations on First Philosophy.

Steup, Matthias. "Epistemology." Stanford Encyclopedia of Philosophy. 14 December 2005. 21 April 2009