Descartes separates external objects into those that are clear and distinct and those that are confused and obscure. The former group consists of the ideas of extension, duration and movement. These geometrical ideas cannot be misconstrued or combined in a way that makes them false. For example, if the idea of a creature with the head of a giraffe, the body of a lion and tail of a beaver was constructed and the question asked if the creature had a large intestine, the answer would have to be invented. But, no mathematical re-arrangement of a triangle could allow its three internal angles to sum to anything but 180 degrees. Thus, Descartes perceived that truths may have a nature or essence of themselves, independent of the thinker. In Descartes' formulation, this is a "mathematical" truth only pragmatically related to nature; the properties of triangles in Euclidean geometry remain mathematically certain.