Since classical times, the dialectic of Art and Nature has found expression in architectural theories and practices that have claimed for the preeminent craft of Architecture the discovery of a system of correct design, construction, and ornament grounded in natural laws. The intellectual arguments that have made such systems plausible are rooted in assumptions about legitimacy in the choice and use of materials of construction, and assumptions about the right relationship of materials to structural function. Imaginative and ethical literature have most fully articulated these assumptions, although modernist architectural rhetoric sustains and renews them. In the Stoic eye, all craft is suspect as an illegitimate reordering of natural forms and natural processes; medieval esthetic systems may classify architecture as the bastard child of man and nature. The most effective and pervasive mechanism by which architecture has circumvented such strictures is the functionalist formula that in essence requires identity of content with form, of dweller with dwelling, of hollow with shell, as both a physical and a metaphysical unity. Such a metaphoric formula is realized fully only in imagination, finding its fullest expression in English estate poetry of the 17th century. There, a complex set of literary devices permits the formulation of ideal structures in conformity with natural law, however defined, drawing on broad paradisal myths as well as narrower historical and architectural quarrels to establish a permanent dichotomy between the "natural," "functional" structure and its contrary. In the exaltation of form over content, and in the rehabilitation of luxury in construction, modern architectural theory and practice has radically modified the classical formula, while retaining its essential terms.