Hossein Jorjani
First publication: 2026 – 06 – 30
In Aristotelian logic, the species infimae (“lowest species”) occupied the final level of the genus–species hierarchy—the most specific universals that could still apply to more than one individual. They marked the boundary between universal and particular, serving as the lowest kinds that could figure in scientific demonstration. Philosophically, they provided the foundation of definition and knowledge, since science (epistēmē) concerned species rather than individuals. Bacon retained the term but reoriented its function: the species infimae became for him not the terminus of logical subdivision but the starting point of empirical analysis—the smallest and most stable perceptual kinds from which sound induction could begin.
In Aristotle, genus and species were logical and metaphysical categories, defining conceptual relations of inclusion based on essential differences. Linnaeus later adopted these terms for empirical taxonomy, transforming them into morphological groupings of organisms. The Linnaean hierarchy thus preserved Aristotle’s vocabulary while transforming its function: what had been a structure of concepts and essences became a classification of observable kinds. Bacon’s use of species infimae anticipates this transition, standing midway between Aristotelian definition and empirical classification.
This essentialist framework persisted into Linnaean taxonomy, though applied empirically rather than metaphysically. Darwin’s theory of evolution later dissolved the Aristotelian and Linnaean conception of species as fixed kinds by grounding classification in historical genealogy rather than in static form or morphology. From that point, species and genus ceased to designate fixed logical or morphological ranks and became relational nodes within evolutionary history. In this long trajectory, Bacon’s species infimae occupy a transitional position—anchored in observation yet still committed to the search for stable natural kinds.
In the twentieth century, evolutionary philosophers such as David Hull advanced a further transformation by arguing that species are not classes but individuals—spatiotemporally continuous entities unified by genealogical relations rather than by shared essences or properties. This “individuality thesis” replaced the typological logic of Aristotle, Linnaeus, and even Darwin’s early formulations with an ontology of historical process. In this light, Bacon’s species infimae may be understood as an important transitional stage in the long transformation of the concept of species—from universal forms, through empirically grounded yet still essentialized kinds, to historically individuated evolutionary lineages.
Hossein Jorjani 