Only with present imaging can this topic be dealt with properly as
rightly understood there are two types of retrogrades which
distinguish the motion of the inner planets from the outer planets.

As the inner planets of Venus and Mercury swerve around the Sun they
appear to move forward as they come from behind the Sun and then move
in an opposite direction again st the background stars when hurtling
in front of the Sun as they overtake our planet -

http://www.masil-astro-imaging.com/S...age%20flat.jpg

The retrogrades of the outer planets are different and the perspective
of a faster moving Earth overtaking these planets generates the
familiar forward-backward-forward motion -

http://apod.nasa.gov/apod/ap011220.html

Of course,these easily understood perspectives do not rely on a
ridiculous empirical view that has no astronomical value whatsoever -

"For to the earth planetary motions appear sometimes direct, sometimes
stationary, nay, and sometimes retrograde. But from the sun they are
always seen direct,..." Newton

The misguided perspective of empiricists has proven far more difficult
to overturn than a geocentric view as the nature of their agenda is
homocentric by virtue that they reference everything against a
rotating celestial sphere,however,the fertile ground of contemporary
imaging is the real decider in what is true and what is not - it only
takes people with a genuine love and feeling for astronomy and the
celestial arena to make sense of different types of retrogrades using
different perspectives of motion.