So, a RESTful service has a fixed set of verbs in its vocabulary. A RESTful web service takes these from the HTTP methods. There are some supposed advantages to defining a fixed vocabulary, but I don't really grasp the point. Maybe someone can explain it.

Why is a fixed vocabulary as outlined by REST better than dynamically defining a vocabulary for each state? For example, object oriented programming is a popular paradigm. RPC is described to define fixed interfaces, but I don't know why people assume that RPC is limited by these contraints. We could dynamically specify the interface just as a RESTful service dynamically describes its content structure.

REST is supposed to be advantageous in that it can grow without extending the vocabulary. RESTful services grow dynamically by adding more resources. What's so wrong about extending a service by dynamically specifying a per-object vocabulary? Why don't we just use the methods that are defined on our objects as the vocabulary and have our services describe to the client what these methods are and whether or not they have side effects?

Essentially I get the feeling that the description of a server side resource structure is equivalent to the definition of a vocabulary, but we are then forced to use the limited vocabulary in which to interact with these resources.

Does a fixed vocabulary really decouple the concerns of the client from the concerns of the server? I surely have to be concerned with some configuration of the server, this is normally resource location in RESTful services. To complain at the use of a dynamic vocabulary seems unfair because we have to dynamically reason how to understand this configuration in some way anyway. A RESTful service describes the transitions you are able to make by identifying object structure through hypermedia.

I just don't understand what makes a fixed vocabulary any better than any self-describing dynamic vocabulary, which could easily work very well in an RPC-like service. Is this just a poor reasoning for the limiting vocabulary of the HTTP protocol?