The Supreme Court, examining whether states can sub-classify scheduled castes and scheduled tribes for grant of quota inside quota, on Wednesday said all SCs and STs may not be homogenous in terms of their sociological, economic, education and social status.

"They (SCs and STs) may be a class for a certain purpose. But, they may not be a class for all the purposes," a seven-judge constitution bench headed by Chief Justice DY Chandrachud observed while hearing as many as 23 petitions on the issue.

The top court is hearing references to revisit a five-judge constitution bench judgement of 2004 in the case of 'EV Chinnaiah vs. State of Andhra Pradesh' in which it was held that SCs and STs are homogenous groups and hence, states cannot further sub-classify inside SCs and STs to grant quota inside quota for more deprived and weaker castes in these groups.

"Therefore, there is homogeneity in the sense that each one of them belongs to the scheduled castes. But your argument is that there is no homogeneity either in terms of the sociological profile, economic development, social advancement, education advancement.

"There is heterogeneity in terms of past occupation... social status and other indicators may be different for different castes inside the Scheduled Castes. So, the degree of social and economic backwardness may vary from from one person or caste to another," said the bench also comprising justices B R Gavai, Vikram Nath, Bela M Trivedi, Pankaj Mithal, Manoj Misra and Satish Chandra Mishra.

Solicitor General Tushar Mehta, appearing for the Centre, opposed the findings of the Chinnaiah judgement and said it disempowered the State to frame appropriate policy by sub-classifying the zone of reservation appropriately and diminishes the constitutional guarantee of equality of opportunity.

"The central government is committed to the declared policy of reservation for backward classes as a measure of affirmative action to bring equality to those who have suffered hundreds of years of discrimination," he said.

At the outset of the second day proceedings, senior advocate Kapil Sibal argued in favour of the states being empowered to sub-classify SCs and STs to ensure substantive equality among the deprived classes.