Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_24508 ( "District" text, "Vacator" text, "Reason for change" text, "Successor" text, "Date successor seated" text )

### Question ###
Name the number of reason for change on may 11, 1939

### Accurate SQL ###

SELECT COUNT("Reason for change") FROM table_24508 WHERE "Date successor seated" = 'May 11, 1939'