From this thread, a perspective on types:
My conclusion is that less strongly typed (i.e., dynamically typed) systems are the ultimate type systems, because they allow growth and change, while preserving the ability to use machine reasoning about types. strict type systems, where every "object" is a type, do not scale well because the computer is not involved in the typing decisions, only in checking them. still, some of the lessons of "object-oriented" programming in the Algol family can be fruitfully employed in dynamically typed systems.
Essentially, it is the a priori aspect of strongly typed systems that is fundamentally unsuited to the process of acquiring the knowledge of the types necessary to implement them and relate them correctly.