This laconic discourse uses the Aristotelian authority to define the role of the analogical procedure in the government of the architectural composition. Respecting its ambiguous balance between mathematical method and attitude of the imagination, analogy is here intended as the relationship between fragments of the structure and the structure in its entirety. Specifically, it is considered as a procedure through which the human being is capable to mutually associate entities of different nature to process and elaborate formal similarities and differences. The philosophical tradition, since beginning of time, introduces this associative model to emancipate the primitive concept of comparison between two entities from a mere “formal similarity between the entities themselves” to a “proportional correspondence between a couple of measures of different entities “. The treatises of Humanism, following the Vitruvian though congenitally permeated by Aristotelian philosophy, introduce in architecture a system of general validity to overcome any particular approach coming from the visual association of apparent or evident forms. ‘Ça va sans dire’ that the analogy permeates every discourse on architecture and, more or less explicitly, guides every project practice from its genesis to its signification. Not accidentally, Vitruvius literally uses the Greek word ‘analogon’, only later translating it into Latin ‘proportio’. As a proportion he means the correspondence between the measures of the different elements that make up a single work. ‘Analogon’ is thus an instrument necessary to mathematically regulate the principles of the design of a building, specifically a temple. Vitruvius therefore intends analogy as a function related to logical-dialectical rather than to the universe of sensory perception. Therefore, he means the analogy in a very different sense and meaning from the intuitive one that will then use the romantic aesthetic and modern philosophy. The analogical procedure for Vitruvius is the “way” through which the elements of the order are regulate, as it was for Aristotle the way to construct the proportional metaphor, considered “the mother of all the rhetorical figures”. In these terms the analogy works as a “proportioning machine” between different entities, but it is not to be considered as an idea of universal metaphysical order. Following this logic construction, it could be said that for Aristotle the human being is an “analog machine”. This machine proceeds by processes of affinity and similarity, sometimes through linguistic metaphors abstracted from the “logic of facts”, to operate according to what is properly defined as “logic of opinion”. The logic of opinion, or even more properly, the “logic of affection”, is constituted through a continuous game of analogies with the “world of the surrounding and memory”, therefore with the objects of the outside reality and their inner representations. The affinities that are established between objects, then between architectures, arise from external, formal relations, subsequently become affective, sympathetic, finally spiritual. It is this aura of spirituality that paradoxically brings them closer to the abstraction of the Euclidean analogy.