Natural signs are those which make another thing known without any will or desire of signifying anything, the way that smoke signifies fire. For smoke does not signify because it wishes to; rather, through observation and contemplation of things experienced it is known that where smoke can be seen, there is fire beneath it. The footprint of a passing animal pertains to this genus. And the affections of a sad or angry soul are signified in the face independently of the sad or angry person's will. And any other movement of the soul may be given away on the face's indication, whatever our will in the matter.
On Christian Teaching 2.I.2, ca. 397 (rev. 427)
On Christian Teaching 2.I.2, ca. 397 (rev. 427)
