Before taking a look at this article, I would like to mention that this topic goes beyond the basic knowledge of Human Design. Please take your time to read carefully because it can get complicated in some places. If you don't know your substructure, please contact a professional reader or use an online tool that displays it. For example www.bodygraph.io
In the substructure of the human design system, we find really fascinating things. Yes, the surface is already incredibly deep and precise, but if we look beneath the lines of the gates, we can discover color, tone and base and thus the variables that are determined from the tonal level of sun + earth & nodes.
Let me put it simply: For example, if you have a 1st, 2nd or 3rd tone beneath your Sun-Earth Lines it is automatically LEFT and if you have a 4th, 5th or 6th tone it will be RIGHT. This can be shown in the bodygraph as a left or right arrow (in some cases also as R/L). This describes the binary principle of ACTIVE or PASSIVE - YANG or YIN. We find this binary everywhere in HDS - everything has at least two sides. Just feel into this fact the next time you look at your chart.
If we now look beneath the surface, beyond the design Sun-Earth (that is the left side), we discover the world of PHS - the "Primary Health System". This variable aspect (one arrow out of four), whether LEFT or RIGHT, describes how the brain functions - ACTIVELY or PASSIVELY. This may sound complex, but it really makes a lot of sense. An active brain has a high metabolism, therefore needs more food and is constantly active - this gives it the ability to always have the important things in its memory; in other words, to be able to retrieve them.