Meditations on First Philosophy is a work written by 17th century French author Rene Descartes that discusses six "meditations" on the truth that humanity can decipher from the natural world. The subjects under consideration range from youthful falsehoods to the existence of a God. Indeed, many of Descartes' ideas are controversial, as you cannot prove a negative, but they are revolutionary for the time the work was written.
The first of the six meditations discusses how the author, Descartes, came to know the simple truths in life. The example of love can be given here. As a young child or even a young adult, Descartes does not know exactly what love is. However, as he matures, he finds out the truth using his senses. Descartes says the same is true for many things - "truth" can be found using the senses, as they are the connection between the mind, body, and the real world.
In the second meditation, Descartes discusses exactly what was mentioned prior - the mind and body. He believes that the mind and body are very separate, and the body knows more about the mind than the mind knows about the body. In ways, the mind is in a separate realm of existence, completely separate from body and the Earth on which it lives.
Descartes claims to prove the existence of God in his next meditation in evaluating the extent to which the world is perfect. He claims, as many have over generations, that something cannot come from nothing. Using this knowledge, and the assumption that God is perfect, he says that he himself, as well as all other humans, must have been created by God. This is because, he says, he could not have been created by himself, as he would made himself perfect, and he could not have been created by his parents, which are non-perfect life forms.
Next, Descartes tackles how the world can have evil with a good God in it. He claims that humans are in the middle of two extremes - one being God, which is perfect, and the other being nothing, which is the deepest form of evil. Humans must, therefore he claims, be a mixture between the two, as they are neither nothing nor perfect.
In his fifth meditation, Descartes explains the gap between the consciousness and material things. For example, you may be able to see that an animal exists, but does that body represent its consciousness? In the era of Descartes, the advent of technologies that would allow goods to be transferred resulted in many more material objects, which explains the other half of his ponderings - the true meaning that some people feel that material is worth more than mind (emotions and love).
In his next meditation, Descartes extends this argument, saying that there is a large gap between humans and the material world in which they live. This meditation is similar to meditation two, as it discusses both the mind and body (the body being material things).