It is possible, nevertheless, to communicate ideas to deaf men, and even to give them precise notions of general subjects, by means of signs, and by writing. A person born deaf, may be taught to read, to write, and even by the motion of the lips to understand what is said to him; a plain proof how much the senses resemble, and may supply the defects of each other.
On this subject it may not be improper to quote a fact, of which I was myself a witness. One M. Pereire, a native of Portugal, who had made it his particular study to teach persons born deaf and dumb, brought to my house a young man who was thus unhappily circumstanced. He was at the age of nineteen, in the month of July, 1746, when M. Pereire undertook to teach him to speak and read. More than four months had not elapsed, when he was capable of pronouncing syllables and words; and in the space of ten months, he perfectly understood, and could, with tolerable distinctness, pronounce about thirteen hundred different words. This education, so favourably begun, was interrupted for nine months by the absence of the master; who then found him far less intelligent than he had left him. His pronunciation was vitiated, and of the words he had learned most of, he retained not the smallest remembrance. M. Pereire accordingly renewed his instructions in the month of February, 1748; and from that time he never left him till June 1749. At one of the meetings of the French Academy this young man was brought them, and had several questions proposed to him in writing. To these his answers, whether written or verbal, were highly satisfactory. His pronunciation, indeed, was slow, and the sound of his voice was harsh; but at these defects there is little cause to wonder, as it is by imitation alone that our organs are enabled to form precise, soft, and well-articulated sounds, and, as this young man was deaf, he could not be expected to imitate what he did not hear; but which harshness, by the assiduity and skill of his master, might, however, in some degree, be corrected afterwards.
In the above case, the expedition of the master, and the progress of the pupil, who indeed seemed to be no wise deficient in point of natural ability and understanding, are an ample proof, that persons born deaf and dumb may, by art, be brought to converse with other men; and I am persuaded that, had this young man been instructed so early as at the age of seven or eight, he would have attained as great a number of ideas as mankind possess in general.