Numbers and numerosities: Absence of abstract neural realization doesn't mean non-abstraction

The neural realization of number in abstract form is implausible, but from this it doesn't follow that numbers are not abstract. Clear definitions of abstraction are needed so they can be applied homogenously to numerical and non-numerical cognition. To achieve a better understanding of the neural substrate of abstraction, productive cognition - not just comprehension and perception - must be investigated.