As in a dream, all external objects perceived with the five senses are not there; they are mental fabrications. As in a magic show, things are made to appear by a temporary conjunction of causes, circumstances and connections. As in a visual aberration, things appear to be there, yet there is nothing. As in a mirage, things appear but are not real. As in an echo, things can be perceived but there is nothing there, either outside or inside. As in a city of clouds, there is neither a dwelling nor anyone to dwell. As in a reflection, things appear but have no reality of their own. As in an apparition, there are all sorts of forms but they are not really there.

-- Patrul Rinpoche