Contrary to the rationalists' claims about the deeper reality of the ideal forms at the base of our thinking, concepts are actually just mental models that may help us to organize our memories in useful ways - ways that make it easier for us to plan and then act. We invent them and try them out and if they help us to get results, we keep them. When they don't seem to be working anymore, we nearly always just drop them and look around for newer, better tools. 

Even ideas of numbers, Descartes’s favourite “clear” ideas, are merely mental tools that are more useful than ideas of Ents. Counting things helps us to act strategically in the material world and thus to survive. Imagining Ents gives us temporary amusement—not a bad thing, though not nearly as useful as an understanding of numbers.

But numbers, like Ents, are mental constructs. In reality, there are never two of anything. No two people are exactly alike, nor are two trees, two rocks, two rivers, or two stars. So what are we really counting? We are counting clumps of sense data that match concepts built up from memories of experiences, concepts far more useful in the survival game than the concept of an Ent. 

Even those concepts that seem to be built into us (e.g., basic language concepts) became built-in because, over generations of evolution of the human genome, those concepts gave a survival advantage to their carriers. Language enables improved teamwork; teamwork helps us to get things done. Thus, as a physically explainable phenomenon, the human capacity for language also comes back into the fold of empiricism.

Geneticists can locate the genes that enable a developing embryo to build a language centre in the future child’s brain. Later, an MRI scan can find the place in your brain where your language program is located. If you have a tumor there, a neurosurgeon may fix the “hardware” so that a speech therapist can help you to fix the program. In other words, even the human capacity for language is an empirical phenomenon all the way.²

   

                                          Stone Age (artist: V. Vasnetsov)                (credit: Wikimedia Commons)

In the meantime, millenia ago, counting enabled more effective hunter behavior. If a tribe leader saw eight of the things his tribe called deer go into the bush and if only seven came out, he could calculate that if his friends caught up, circled around in time, and executed well, and if they worked as a team and killed the deer, this week the children would not starve. Both the ability to count things and the ability to articulate detailed instructions to the rest of one’s tribe boosted a primitive tribe’s odds of surviving.

Thus were the rudiments of arithmetic and language built up in us. Those who used them survived in greater numbers than those who didn't. 

If the precursors of language seem to be genetically built into us—for example, human toddlers all over the world grasp that nouns are different from verbs—while the precursors of math are not, this fact would only indicate that basic language concepts proved far more valuable in the survival game than basic math ones. (Really useful concepts, like our wariness of heights or snakes, get written into the genotype.) The innate nature of language skills indicates that neither basic language concepts nor basic arithmetic concepts are coming to us by some mysterious, inexplicable process out of Plato’s ideal dimension of the Good. All these human traits have scientific explanations.