On Christian Doctrine

3. Conventional signs, on the other hand, are those which living beings mutually exchange for the purpose of showing, as well as they can, the feelings of their minds, or their perceptions, or their thoughts. Nor is there any reason for giving a sign except the desire of drawing forth and conveying into another’s mind what the giver of the sign has in his own mind. We wish, then, to consider and discuss this class of signs so far as men are concerned with it, because even the signs which have been given us of God, and which are contained in the Holy Scriptures, were made known to us through men—those, namely, who wrote the Scriptures. The beasts, too, have certain signs among themselves by which they make known the desires in their mind. For when the poultry-cock has discovered food, he signals with his voice for the hen to run to him, and the dove by cooing calls his mate, or is called by her in turn; and many signs of the same kind are matters of common observation. Now whether these signs, like the expression or the cry of a man in grief, follow the movement of the mind instinctively and apart from any purpose, or whether they are really used with the purpose of signification, is another question, and does not pertain to the matter in hand. And this part of the subject I exclude from the scope of this work as not necessary to my present object.