The silent rhetoric, or rhetoric tacens of art, may include powerful
gestures, but the "silent" gestures of "linear perspective" may be
very eloquent.
This painting by Masaccio follows Alberti's suggestion that there be a
"witness" in every painting. The function of this "witness" is to
reach out to the viewer, and engage the viewer with the scene depicted
in the painting. Masaccio has suceeded in doing this: Mary is the witness
and she looks out of the painting, her eyes engaging the viewer, but Mary
also gestures with her hand, pointing to her crucified son Jesus in the scene.
This "witness"'s gesture is silently eloquent, the more so as perspective is
used to focus upon Jesus and God above Jesus.