What enables signs to be understood is their consistency with the material world. For instance, the sensory sign of the baby is understood because it is consistent with what a baby looks like. In the middle circle, the pointing finger shows that I directed your attention to the baby. Such an act of reference is a common motoric sign. The baby is looking at you.
Linguistic signs depend on consistency of conventional use, i.e., on the grammar of a language.
We call objects like the one at the left, a baby, and such acts as the baby is performing, looking at you. An illustration of the three fundamental kinds of signs in experience. Consider what mere consistency of signs gets us. The miracle of communication is so common that we almost always take it for granted. Only in errors and lies do we realize, to a very slight degree, how absolutely dependent we are on the consistency of signs.