> It's called the "autism spectrum" because it's a spectrum, not a binary. People can share some autistic traits without their rising to the level of a diagnosable disorder. If a person is described as nerdy, introverted and eccentric, they probably are further along on the autistic spectrum than most, while not necessarily having full-blown autism.

I thought it was called a spectrum because of the variation in severity and symptoms among people with diagnosable autistic disorders. As I understood it, if you don't have such a disorder, you're not on the spectrum.

I think you are getting into a map/territory issue.

We think of it as a spectrum because we observe a spectrum among people with diagnosable autistic disorders.

However, we do not have a fundemental understanding of what autism is, or a binary test to detect it. This would imply that in reality there is a spectrum that extends beyond the diagnosable region(s) we have.

The disorders do not cleanly cleave away from non-autistic. It really can be a judgement call at times.

Absolutely. But that's not, as I understand it, why it's called a spectrum. It's called a spectrum because it covers conditions as different as Asperger syndrome (which often isn't diagnosed until adulthood, and may never get diagnosed at all) and childhood disintegrative disorder, where the onset of symptoms is so sudden and dramatic that the child themselves may notice and ask what is happening to them.

Being "nerdy, introverted and eccentric" doesn't necessarily mean you are on the spectrum. It may do: you may have an ASD, diagnosed or undiagnosed. But it may just mean you are nerdy, introverted or eccentric.