An Illustration of Nominalism
Words, IMO, are simply linguistic conveniences for organizing categories of attributes in different entities. For instance, if I observe a certain configuration of attributes in the bloods of many people, I can then, for purposes of classification, designate them according to types.
The spectrum of autisms (or autism spectrum), as the term is commonly used by researchers, includes Kanner’s Autism, Asperger’s Autism, and PDD-NOS. As long as that term continues to have a pragmatic value in describing variance, it will likely continue to be used (and many writers predict it will be incorporated into the DSM-V). If more attributes are discovered, which do not fit into this present-day construct, then the term will either be redefined or replaced with something else.
It may also end up that the “leftover” symptoms are defined as something else, which is then defined as a comorbid condition…
Add CDD and Rett’s to the list, by the way.