The usefulness of a theoretical structure lies in its concreteness and in the precision with which questions can be formulated. The more precise the questions, the easier it is to compare theoretical consequences with experience. An approach that has been very successful is to find the minimum number of assumptions that imply as logical consequences the qualitative features of the system that we are trying to describe. If we pose the question this way, it means that we agree to simplify. As Albert Einstein once said, “Make things as simple as possible, but no simpler”. Of course, there are risks, and it is here that science becomes as much art as logic. One risk is that we simplify too much and in the wrong way, that we leave out something essential. This is the intellectual risk. Another risk is political – that we may choose to ignore in the first approximation some facet that an important individual has spent a lifetime elucidating.