Plato says that that is an object of sensation, which is never stationary either as to its quality or its quantity, but which is always flowing and changing; as, for instance, if one take from any objects all number, then one cannot affirm that they are either equal, or of any particular things, or of what quality or quantity they are. [...] On which account he says, that ideas exist in nature as models; and that all other things are like them, and, as it were, copies of them. [...] Plato, in his theory of Ideas, says, “That since there is such a thing as memory, the ideas are in existent things, because memory is only conversant about what is stable and enduring; and that no other thing is durable except ideas, for in what way,” he continues, “could animals be preserved, if they had no ideas to guide them, and if, in addition to them, they had not an intellect given to them by nature?” But as it is they recollect similitudes, and also their food, so as to know what kind of food is fit for them; which they learn because the notion of similarity is implanted naturally in every animal; owing to which notion they recognize those of the same species as themselves. — Diogenes Laertius, *Lives of Eminent Philosophers*, Book III, Section XII, trans. C. D. Yonge (1853). **Surface Gloss:** Quoting the Sicilian historian Alcimus, Diogenes argues that sensible things constantly mutate, whereas eternal Ideas serve as stable models; without an innate grasp of these stable models through memory, living creatures could not even recognize food or their own species. **The Survival Proof of Abstractions:** When hard-headed pragmatists dismiss abstract models or "theory" as useless luxury, flip the burden of proof onto memory and pattern recognition. In a data environment of total flux, no organism or organization can identify "food" or "kin" without a stable, pre-loaded template that outlasts the changing data stream.
— In our words · Source: Lives of Eminent Philosophers (Diogenes Laertius)