A fundamental question in epistemological philosophy is whether reason may be based on a priori knowledge—that is, knowledge that precedes and which is independent of experience. In modern science, the concept of innateness has been associated with particular behaviors and types of knowledge, which supposedly have been present in the organism since birth (in fact, since fertilization)—prior to any sensory experience with the environment. This line of investigation has been traditionally linked to two general types of qualities: the first consists of instinctive and inflexible reflexes, traits, and behaviors, which are apparent in survival, mating, and rearing activities. The other relates to language and cognition, with certain concepts, ideas, propositions, and particular ways of mental computation suggested to be part of one’s biological make-up. While both these types of innatism have a long history (e.g., debate by Plato and Descartes), some bias appears to exist in favor of claims for inherent behavioral traits, which are typically accepted when satisfactory empirical evidence is provided. One famous example is Lorenz’s demonstration of imprinting, a natural phenomenon that obeys a predetermined mechanism and schedule (incubator-hatched goslings imprinted on Lorenz’s boots, the first moving object they encountered). Likewise, there seems to be little controversy in regard to predetermined ways of organizing sensory information, as is the case with the detection and classification of shapes and colors by the mind. In contrast, the idea that certain types of abstract knowledge may be part of an organism’s biological endowment (i.e., not learned) is typically met with a greater sense of skepticism. The most influential and controversial claim for such innate knowledge in modern science is Chomsky’s nativist theory of Universal Grammar in language, which aims to define the extent to which human languages can vary; and the famous Argument from the Poverty of the Stimulus. The main Chomskyan hypothesis is that all human beings share a preprogrammed linguistic infrastructure consisting of a finite set of general principles, which can generate (through combination or transformation) an infinite number of (only) grammatical sentences. Thus, the innate grammatical system constrains and structures the acquisition and use of all natural languages.