Meditation 6

In chapter 6 of the meditations Descartes uses this chapter to talk about the real distinction between the mind and the body and the existence of material things. He starts out this part by stating that material things can exist because God is able to make them exist. He goes into talking about how since he can clearly grasp something (pure mathematics) they must therefore exist. Knowing the existence of such objects is possible and he goes into trying to prove this by using the idea of mental images. He does this by drawing a distinction between mental images and understanding. Descartes uses an example to further this point.
“When I have a mental image of a triangle, for example, I don't just understand that it is a figure bounded by three lines; I also "look at" the lines as though they were present to my mind's eye. And this is what I call having a mental image. When I want to think of a chiliagon, I understand that it is a figure with a thousand sides as well as I understand that a triangle is a figure with three, but I can't imagine its sides or "look" at them as though they were present.”

I rather agree with Descartes on this idea of distinction between mental images and understanding. There is definitely I difference between the two ideas and I sort of have a example of this. I can imagine a unicorn that it is a horse that has a horn like a rhino or some other animal with a horn. Though I can imagine this animal because it is made up of other animals I can not truly understand what a unicorn is until I could see one for myself which is impossible.