The senses, the sole source of knowledge, are supposed to yield us immediately cognition of individual things; phantasy (which Gassendi takes to be material in nature) reproduces these ideas; understanding compares these ideas, which are particular, and frames general ideas.
In effect, all that happens with suggestion is that the person creates an exciting phantasy within the emotional sequence of abreaction.
The way to use the phantasy is to let it act itself out during reverie whilst trying to be a neutral observer of it.
But an infantile phantasy needs a bit of examination before it can be admitted to reality.
At Tyre, as among the Hebrews, Baal had his symbolical pillars, one of gold and one of smaragdus, which, transported by phantasy to the farthest west, are still familiar to us as the Pillars of Hercules.