Quid sit differentia, a rather finite disputation within the voluminous treatise known as the Placita philosophica, presents a specific aspect of the cognitive process of the Baroque architect Guarino Guarini (1624–1683), through the presence of light and the mysterious counterpart of shadow. Difference, according to Guarini, is defined as a metaphysical composition which generates form into the physical field of perception. This point is fortified through another disputation in Book Six of the Placita philosophica, entitled “On the miraculous architecture of the eyes” (De oculi mirabili architectura), which expounds upon Guarini’s profound knowledge of light and optical theory with a great deal of intricacy, representing the anatomical constituents of the eye as a reflection of externalized architectural form. The architectonic structures described within the interior anatomy of the eye, reflect the external realm of Guarini’s cosmology, and his utilization of the Vitruvian principles of the art of building, the study of light and the mechanical movement of the universe.

Noé Badillo received his PhD in the history and theory of architecture in 2021 from Arizona State University. His research is driven by a long-standing fascination with the nature of light and perception, within art, architecture, and the human mind. His dissertation on the Italian Baroque architect Guarino Guarini, entitled “Geometry of the Sun: Guarino Guarini and the Church of San Lorenzo,” is also about light, and the complex use of mathematics within architecture and cosmology. Badillo is also a professional artist, whose work was most recently exhibited in Venice, Italy, during the 2022 Biennale.

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