Augustine divides the sign into the two main classes of natural signs (signa naturalia) and given signs (signa data). “Natural signs are those which, apart from any intention or desire of using them as signs, do yet lead to the knowledge of something else”,[8] as, for example, smoke when it indicates fire, the footprint of an animal passing by, or the countenance of an angry or sorrowful man. “Conventional signs, on the other hand, are those which living beings mutually exchange in order to show, as well as they can, the feelings of their minds, or their perceptions, or their thoughts.”[9] Whether and to what extent such an “intention to signify” (voluntas significandi) can be assumed in cases of animal sign communication Augustine leaves open.[