the way i see it insticts are based on stages of developement, because the enneagram is expressed through the stage one is at, or the stage one adapted to in his culture. but since people who use the instinct system dont understand stages they interpret the instincs in different ways. most of the time they intuit the stages, because stages are pretty damn obvious (just not recognizable as such, unless you get them), but there are lookalike effects between several stages, so things get confused. the stages are
1) merged (childlike, think of aborigines, dreamtime),
2) impulsive (self preserving, fighting for personal space and power, conquering, pragmatic instable powerbased social order),
3) conformistic (social, status, family, heritage, community, persona, cultivating, missionary, introspection largely limited to adaption/moral issues),
4) rational (could look like any of the three instincts, depending on situation, some refined sense of psychology, but focus on external/behavior, manipulation of the self for external purpose),
5) pluralisitc (is rather introspective, adapts life to self, therefore sensitive to individuality, therefore gets most out of relationships (much like sexual instinct), but is also very social - sees the individuals in groups, though, is worldcentric and therefore loves to travel and connect with most cultures on a mutual basis),
there are further stages but they are rare ...
like with instincts, people are never exactly and only on one stage at a time. they are mixed packages internally, but also usually focus on one stage externally.