Question: Is there a reason why there's no subject heading for Shabta'ut  (Shabbateanism, Shabbatean movement, Sabbateanism) but only for Sabbathaians? An OCLC title keyword search for shabta'ut retrieved 20 records, the vast majority of which were assigned the heading for the class of persons even though the works appear to be about the movement.
Wouldn't it be nice to assign a heading like: "Sabbateanism--Social aspects" to the book  Shabta'ut : hebetim hevratiyim ?

Answer: It seems that some older headings for specific sects have been established in a form we now consider to be a
"class of persons."

The heading "Sabbathaians" has "Jewish sects" as a broader term, and despite its structure, was intended to refer to the movement.  CPSO's historical subject heading files might provide the rationale for this--probably literary warrant--"ism" words are a lot more popular now.  By today's standards, such a heading seems to defy the principle of specificity, but by earlier standards this heading could have been considered esoteric, and sufficient for the topic.
 
We had a similar situation with the heading "Karaites."  CPSO approved a change to add 450's for various names for the movements (Karaism and Karaitism) to those for the variants for the class of persons.  A scope note was also added, "Here are entered works on the Jewish sect known as Karaites and works on its adherants as a class of person."  This change enabled us to continue to assign the heading as it had been in the past, without necessitating additional bib file maintenance.

The Karaite approach may or may not be the best solution in this case.  Someone could propose a new heading, but would need to consider the bib file mainenance implications.  Also, the BT should be reconsidered, as well--"Jewish messianic movements" may be a better BT than "Jewish sects."

Lenore