When Mercury is retrograde in a natal chart the interpretation can include challenges to or out-of-the-ordinary manifestations of the typical associations with Mercury.  When I'm covering the general retrograde phenomenon in my classes and workshops, I often encourage students to think of retrograde as "repressed expression" (mnemonically Rx).  This easy to remember phrase triggers our thoughts to consider that the normal effects of the involved planet are not expressed easily or without being modified by some other (often underlying) influence.  

Mercury Rx natally may sometimes suggest speech challenges or idiosyncrasies (Mel Tillis), thinking and communicating in an unusual manner (Harpo Marx), or difficulty expressing ones self -- needing an "interpreter" to make him/herself understood -- sometimes being on a totally different wavelength intellectually (Michel Nostradamus, Salvador Dali, Rod Serling, George Carlin, Steve Martin, Billy Crystal, Howard Cosell, Alex Trebek). This in no way implies that people with Mercury Rx natally are slow learners -- they just approach things differently than others.  This actually makes perfect sense.  After all, Mercury  doesn't really slam on the brakes and hang a U-turn.  It's all in our perspective of what is happening.

Not infrequently, however, people with Mercury Rx natally may be reluctant to share or communicate what's going on in their heads (Howard Hughes).  They may have learned  over time that it is often easier to keep their thoughts "under cover" rather than be forced to repeatedly explain, risk criticism, or even be ridiculed for their different perspective.  They may indeed have a very unique frame of reference for experiencing everything that surrounds them (Stevie Wonder). Interestingly, some people with natal Mercury Rx absolutely seem to be totally in-tune during Transiting Mercury Rx periods and things go incredibly smoothly for them.

Similarly, the other personal planets, including Venus, Mars, and Jupiter -- the Sun and Moon are never Rx -- often exhibit this "repressed expression" of their normal areas of influence.  The outer planets, Uranus, Neptune, and Pluto move so slowly that the retrograde phenomenon is rarely of much importance in natal interpretation, while the effect may be of note when evaluating generational tendencies.

What about Saturn Rx, you ask?  Well, that is too large a topic to get into in this column -- I'll save it for a section of its own at a later date.