Gopal S : the parameter which is required to be applied to SC/STs wrt 15 and 16 is historic untouchability. Becuase there has been a general sense that social and educational backwardness is the determinant of SC/ST. that's not true, for being an SC/ST it is about historical backwardness and its constitutional attornment for the discrimination, so determining who an SC is ( as per decision in Mary Chandrashekhar para 9 ) it says that it is the historic untouchability that is for the determination of SCs , social and educational backwardness define in 366 article, came in by way of amendment after the Indra sahwney judgement