This is what the Astrology Weekly site says about arabic parts"
Robert Hurtz Granite in his book "The Fortunes of Astrology" described how the Lots or Parts were all derived from Equilibrium charts. So any formula with minus Sun in it was derived from the Solar Equilibrium chart, any formula with minus Moon in it was derived from the Lunar Equilibrium chart, any formula with minus Mercury was derived from the Mercury Equilibrium chart and so on.
Your post on Arabic Parts is the first I have ever seen (other than Robert Hurtz Granite) that describes this process. I am so thrilled as so many people really do seem to misunderstand what Arabic Parts are all about.
For those of you who have Solar Fire V5 or Deluxe, it is easy to see this clearly by creating an Equilibrium chart for the Sun, then the Moon and so on. The procedure is as follows:
Equilibrium charts can be emulated using "Multiwheel Superimposition" - which is included in Solar Fire v5 and Deluxe.
To do this
1) You must first have two separate copies of the chart to work with (you can use Chart / Edit / Copy & Edit to create an identical copy).
2) Display these two identical charts in a biwheel.
3) Use RH mouse click and choose "MultiWheel Superimposition", and set the following options
Superimposition type: By exact position of Selected Points
Superimposition options: Base point Ascendant. Superimposition point Sun (or Moon, Mercury etc depending upon which equilibrium chart you want to work with)
Click 'Display Superimposed Positions'
Then click OK
You will now see that the outer chart has been rotated so that the outer Sun is on the inner Ascendant, thus making the outer chart equivalent to the Solar Equilibrium chart. Note that you can change the Superimposition Point for any other planet or house cusp, thus creating any other type of equilibrium chart.
NB - Please remember to reselect Superimposition Type as "Zodiacal (Normal)" when you finish with working with Equilibrium charts. Otherwise all your future biwheels will remain superimposed when you don't want them to be.
So when you use the Solar Equlibrium chart you can clearly see that the position of the Moon in that chart marks the Part of Fortune, the position of Mercury marks the Part of Commerce, the position of Venus marks the Part of Love and so on - as explained in charmvirgo's post.
As you can see, there are literally thousands of Lots when you use each planet's equilibrium chart, but only a few are regularly used. However, all are valid Lots and if any coincide with a planetary degree in your natal chart, or if there are a large collection of them around a natal degree, they will be very powerful.
It is a good idea to print out the equilibrium charts for each planet and keep an eye on them for transits, progressions, directions etc., you can then get a clearer idea of how they work through real life observation.
David Cochrane has written a very interesting article on the Part of Fortune and Part of Spirit on this site:
http://www.astrosoftware.com/ArabicParts.htm
Alice