"We should liberate Greece from Athenian domination! The Thirty Years' Peace must be broken immediately. . . It is the right time to attack! . . . (Sparta, a speaker at the agora, 11th July, 431, B.C.) xxx Athenians! Countrymen! Lend me your ears! I came to speak of peace, not to praise war ... We should keep our word of peace that we signed with Sparta (Athens, a speaker at the agora, 12th July, 431, B .C.) xxxxx Thucydides, the ancient Greek Historian, tells us how Sparta declared war suddenly and the peace was brokendown.. . Of course, sudden changes do not occur only in history but observed in nature and experienced in our daily life also. Phenomena involving discontinuous and sudden changes traditionally have been considered beyond the reach of mathematical analysis. Recently, a branch of mathematics that can deal with the discontinuities has been developed by A. Thom during the 1960s called "Catastrophe Theory". (CT). During the last decades the attention of social scientists have been drawn more and CT has become the target of severe criticisms. This paper views that metamorphotic transformations can be interpreted as "catastrophes" in Thom-Zeeman sense of the term. Hence, the mathematical treatment of metamorphoses requires the use of a new qualitative topological language instead of classical analytical methods. As the author has argued in earlier papers, the existing concepts of cybernetics and system dynamics, based on such concepts as transformations, negative and positive feedbacks, homeostasis or morphogenesis, are not sufficient to cope with the sudden and discontinuous changes; and a new paradigm, the Fourth Cybernetics, should be replaced. (Esmer, 1986, 1989). The first part of the paper shall introduce the basic concepts of CT as a suitable qualitative language for studying and modelling the metamorphic events. The second part shall present the First, Second and Third Generations in the field of city planning that we witnessed during the past decades. In the third part a catastrophe model shall be applied to these changes of paradigms in the city planning field. The fourth part shall aim to evaluate the built qualitative model and to make some guesses for 1990s: Is the Fourth Generation of city planners on the horizon or not?"