...rather than, say, 7 or 23?
I notice that 8 holds special convenience as a power of 2, and also that the 4 functions (T,F,S,N) were "grandfathered in" from Jungian psychology.
However, the question remains - might the psyche not be better described by a different number of functions? I'm aware of the "aspects of reality" argument, but that's an arbitrary division of reality; a theory of personality must describe the workings of the brain.
To aid in considering this problem, I suggest the following features of neuron groups, drawn from a simplistic understanding of neuroscience:
- Distance from sensory inputs
- Self-referentiality (does this neuron group think about itself?)
- Interconnectedness with other brain regions
- Stability of neuron group (meaning slower learning, slower forgetting)