The GoF book is literally a dictionary. I wish more people realised that. It is an attempt at describing a specific "pattern language". A "pattern" is a solu

The GoF book is literally a dictionary. I wish more people realised that. It is an attempt at describing a specific "pattern language". A "pattern" is a solution to a problem that comes up repeatedly in different contexts. For a pattern to be a pattern it there must be a problem you are trying to solve. There must be a context in which you are trying to solve the problem. It must describe the solution in the context. It must describe in which contexts the solution is appropriate and in which contexts it is not appropriate. It must be a solution that is well known and widely used (this bit always surprises people -- usually there is a rule that there must be at least 3 unrelated implementations of the solution in the wild). Finally, for a design pattern, the solution must be in the design domain and not the implemenation domain (drives me crazy when people say that they don't need design patterns because they have a reuse library). A pattern language is a collection of patterns where the use of one pattern commonly implies the use of other patterns. In other words, if you use one pattern in a specific context, then likely certain other patterns will also be useful. Importantly, there are situations where you want to avoid using certain patterns with certain other patterns. The intent of a pattern language is describe these related patterns and how the work (and don't work) together. The GoF book was an example of a possible pattern language for object oriented programming. It was never intended to be an exhaustive pattern language, or a recipe book for implementations. It was simply an example of how you might go about making a pattern language in that domain. It was an amazing achievement because it was the first serious attempt at creating such a pattern language. Unfortunately, not many people have actually read the GoF book end to end and therefore don't really understand what it was for.