When I studied graphic design, teachers always repeated us that we should justify our designs. Every time we presented a project we had a list of justifications; we were selling the design to the teacher. Why we used certain typography, the colors, the size of the pictures and so on.
How can we establish whether a design meets its purpose? Usually we have a pretty good idea of this matter, but we always need to base our judgments, and the best way to achieve this is through an analysis; The Design Process. For example we want to design a logo. First