Mr. Herbert Spencer has made the same proposition as Dr. Potonié and his view briefly expressed is this: “The laws of formal thought are _a priori_ to the individual, but _a posteriori_ to the race.” In other words apriority must be explained by heredity. A dog cannot count, because none of his ancestors have ever counted, but a child has the faculty to learn counting because innumerable ancestors of his have counted and his brain possesses a predisposition to learn counting easily. Concerning our apprehension of space-relations which expressed as mathematical theorems appear to us necessary and are called _a priori_, Mr. Spencer says: “We cannot think otherwise because during that adjustment between the organism and the environment which evolution has established, the inner relations have been so moulded upon the outer relations that they cannot by any effort be made not to fit them. Just in the same way that an infant’s hand, constructed so as to grasp by bending the fingers inwards, implies ancestral hands which have thus grasped, and implies objects in the environment to be thus grasped by this infantine hand when it is developed, so the various structures fitting the infant for apprehension of space-relations, imply such apprehensions in the past by its ancestors and in the future by itself.” Man’s ability to learn counting is inherited, and there may be more or less of it in different people. Mathematical talent is inherited just as much as musical talent or other faculties. But the philosophical question concerning the apriority of mathematical theorems has nothing whatever to do with the origin of mathematical talent. When Mr. Spencer declares that apriority is but an inherited aposteriority, this is equivalent and is intended to be equivalent to an actual denial of all apriority. His very explanation proves that he does not see the real problem, and in the same way Dr. Potonié overlooks it entirely. The philosophical problem of the apriority is not an historical problem, it cannot be solved by tracing the evolution of thought-forms. The philosopher does not ask how did thought-forms originate, but why do we attribute to the laws of formal thought necessity and universality and on what ground can we justify our assumption?