Scheduled Castes constituted a political category of Bengal Hindu population of lower castes considered to be depressed socially and politically. Ever since the morley-minto reforms (1909), under which Bengal Muslims were given the right of separate electorate on account of their political backwardness, the associations of the Hindu depressed classes also had been demanding similar concessions on account of their social and political backwardness.
Such a demand never received any sympathetic support from the indian national congress. Considerations of political ideology and practical difficulties of identification led the Congress to oppose consistently any special political concessions to depressed classes. But the depressed classes of Bengal began to be politically organised under different caste associations and samitis from the beginning of the 20th century, and their demands received sympathetic support from the government. the simon commission Report and the Round Table Conference made specific recommendation for politically accommodating the depressed classes. Finally, the Congress also acceded to their demand under the Poona Pact (1932). In order to avoid psychological stigma attached to the appellation of 'depressed classes' or 'untouchables', the Bengal Government coined in 1932 the term 'Scheduled Castes' for about 76 Hindu depressed castes mentioned in the First Schedule to the India Act of 1935.
The Act defined the Scheduled Castes as 'such castes, races and tribes corresponding to the classes of persons formerly known as the 'depressed classes' as His Majesty in Council may specify'. Under this Act, 20% seats of the Bengal Legislative Assembly were kept reserved for the scheduled castes. Like the Muslims, they also got the right to contest for general seats outside of the seats kept reserved for them. In the elections of 1937, 1946 and 1954, the scheduled castes thus emerged as a powerful balancing force in Bengal politics. All the ministries formed by various political parties from 1937 to 1958 were effected with the support of scheduled caste members in the Assembly. The separate electorate system, as a principle, was abandoned in the constitution of Pakistan (1956). Henceforth, all elections in Pakistan and afterwards in Bangladesh have been holding under the joint electorate system based on universal adult franchise. [Sirajul Islam]