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Following Ledrut’s relationship between form and signification, this paper intends to go beyond urban morphology aporias which reduce forms to their spatial dimension and isolate approaches which should be combined. The urban complex form is the result of the systemic interrelationship between five registers of form: tissue, layout, urban landscape, social form, bioclimatic form; each of them has its specific meaning. Opposed to the morphogenetic approach which emphasizes the urban form continuity, the main historical and morphological periods are marked by discontinuities. Such discontinuities can be evidenced either with Weber’s ideal-typical method, implemented in his analysis of urban evolution, or with Foucault’s notion of “epistemic break”, as a critique of a linear knowledge development. Paris is an example of such a morphological periodisation: the ancient city (Lutèce), the pre-industrial city (medieval and classical), the industrial city (Haussmann and modern city), the post-industrial city. With urban growth, any change in size and/or scale gives birth to a morphological mutation and to a new urban syntax. This set of hypothesis is grounded on ongoing research and it helps to revisit urban morphology as a theory of urban form.