Reason: Essentially the same thing. They're both derived from the eight diagrams used in Taoism, although the ba gua tag seems to be for the full set of eight diagrams, whereas the trigram tag is for when some of the diagrams are absent.
Hillside_Moose said: No, ba gua is the compete set of trigrams. The implication order should be ba_gua -> trigram.
^ That's the right way to do this if we're actually getting an implication out. I question the usefulness of such an implication, but it'll technically be correct.