Over about an 18-month period, Mercury stations retrograde in each element at least twice. It slowly mutates back into the previous element/s for another 18 months – 2-year period. Over a six-year period Mercury will have retrogressed through all the elements in reverse order of the natural Fire, Earth Air, Water. This means that you have a transiting triangulation of Mercury retrograde and direct in your natal chart over about an 18-month period! And, thus it ‘requires’ that you reflect, introspect, and reevaluate the matters pertaining to the 3 houses in which it forms this unique aspect.