306 THE DISCOVERY OF THE CHILD At this stage, therefore, one is perfecting language itself by degrees, as the hearing perceives better the sounds composing words, and the psycho-motor paths are becoming better adapted to articulation. It is this early field of spoken language which has its own beginning and its own course of development leading, by way of perceptions, to the perfecting of the original mechanism of language itself. And at this stage there is established what we call articulate language, which will then be the medium which man will make use of to express his thoughts, and which man will have great difficulty in improving or correcting once it has been fixed. In fact, sometimes higher education is accompanied by imperfect speech, which hinders the aesthetic expression of thought. The development of articulate speech occurs between the ages of two and five—the age of perceptions, in which the attention of the child is spontaneously directed to external objects and the memory is particularly retentive. This is also the age of mobility when all the psycho-motor tracts have become usable, and the muscular mechanism is fixed. At this period of life, by the mys- terious linking up of the auditory tracts and the motor tracts of articulate language, it seems that the auditory perceptions have power to excite the complicated movements of articulate speech, which develops instinctively under these stimuli as if awakening from the sleep of heredity. It is well known that only at this age is it possible to acquire all the characteristic modulations of a language, which it is useless to try and establish later. The mother tongue is pronounced well because it is fixed in childhood, and the adult who learns to speak a new language must carry into it the imperfection which marks the language of the foreigner. Only children who, below seven years of age, learn several languages at the same time, are able to perceive and reproduce the characteristic modulations of accent and pronunciation. In the same way, the defects acquired in childhood, like dialect errors, or others due to bad habits, cannot be cured in the adult.