Lesson held at Quasar Design University during the workshop #www15stanze. In my lecture I spoke about the possibility to create a generative definition useful to create infinite models. In Fact when you think a space like a room, we mean something able to divide an internal space from an external space. Nothing is said about the shape, so, when you create a model 2D or 3D, what you have drawn, is more than your first mental image. The best way to represent a concept is make explicit the algorithm. Grasshopper is a nodal system which make it possible.