There are three instincts described in the Enneagram personality types. What's interesting to me is that they really have no mandatory connection to the personality types themselves and can be understood separately from the enneatypes.

Let's first take a look at the instincts and the two ways they are most often used with the enneatypes.

The instincts are:

• The self-preservation instinct (sp)
• The sexual (sx), one-to-one or intimate instinct
• The social (so) instinct

The more traditional use of the instincts is in reference to instinctual subtypes. This approach sees each of the nine enneatypes as having three subtypes based on each instinct. For example, there would be three subtypes of enneatype 9: the self-preservation 9, the sexual 9 and the social 9. So, although 3 different people can be identified as enneatype 9, if they were different subtypes, their "9-ness" would be influenced by their dominant instinct.

The more recent use of instincts "stacks" them. The three instincts are stacked or ranked according to preference. For example, if the self-preservation instinct is most preferred and the sexual instinct is next preferred then the stacking is sp/sx/so or simply sp/sx (in this case the social instinct is understood as the least preferred because it is left off the stacking). With this approach, each enneatype has six possible instinctual variants.

• sp/sx
• sp/so
• sx/sp
• sx/so
• so/sp
• so/sx

The instincts are often used with the enneatypes to explain why people of the same type seem different. For instance, a self-preservation 9 would be different from a social 9, an sp/sx 9 would be different from an so/sx 9. What seems more interesting to me however is that a self-preservation or sp/sx 9 would be similar to a self-preservation or sp/sx 6 in terms of their instinctual focus. The six variants themselves could be seen as a system of six personality types or variants without any reference to the enneatypes whatsoever.

Adding variants to each enneatype seems a way to not only include other factors that may be useful for understanding personality but also an attempt to compensate for any limitation that only nine types provide.

If I were to add introversion/extraversion into the system, I could create subtypes and variants based on that factor. For example, I could say there is an introverted 9 (i9) and an extraverted 9 (e9). This approach could be used with dozens or even hundreds of  factors and traits. I could use it to introduce those traits into the personality system, but I could also use those traits to rationalize keeping the system at nine types by claiming that any variation within a type is due to those variations of the included factor.

So the questions I raise are:

• What is the basis for nine types besides the fact that there are nine numbers on the Enneagram symbol?
• Is this assumption of nine types limiting the accuracy of the system by not allowing it to adapt and evolve as our understanding does?
• Is the need to retain the magic number of nine types creating complicated workarounds to explain deviations that could better be explained by rethinking the number of types?