How do we type?

Response by David Gray to someone asking, “How is type determined?”

I think you may be asking two questions.
One is: How does one (or how do we) determine what Type someone is? ("motive rather than behavior")
And How does a person become a Type? Nature or nurture?
1) It's often said that it's the motivation, not the behavior, that gives a view into someone's type, but motivations are mainly unconscious. So, it's not a matter of, for example, asking someone why they did X behavior, or some such.
I look at what people incidentally/accidentally express in their worldview and self-image. For example, sometimes a self-typed 4 will express something about how "We're all unique, we just need some encouragement and self-acceptance in order to allow ourselves to express our individuality." Those kinds of "we all" statements, although I'm not saying that no 4 would ever say them, if spoken often enough (and any derivative of this kind of sentiment), would point significantly away from Type 4.
2) I think our enneagram type is part of our genetics.