Speaking politically and historically, the Indian party system has its origins in the nationalist movement for freedom from colonial rule in British India, and incremental extension of franchise since the early twentieth century and introduction of universal adult franchise under the Constitution of independent India enforced since 1950. If democratisation has been the primary causal or independent variable producing the party system we have got today, the Indian social structure with its regional and multicultural variations and the nature of the parliamentary-federal Constitution under which Indian democracy has operated for over seven decades now are the intervening or intermediating variables that have shaped the party system’s patterns and trends. In other words, the primary effects of democratic mobilisation on the party system have been funnelled through the Indian political history and diverse cultural and social setting and the nature of the Indian Constitution. India’s socio-cultural and regional diversities provide a fecund ground for a multiparty system, so does the federal component of the Indian Constitution. However, in the initial decades of post-Independence period the tendency towards multiplication of parties were held in check by the unifying force of the anti-colonial nationalist movement during the British Raj and the presence of the towering charismatic leaders of the nationalist movement at the national and state levels. The parliamentary component of the Constitution, as against its federal component, also exercised a centralising influence and prompted parties to dualistically configure themselves into the government and the opposition. In a parliamentary-federal system like India’s the effects of the two components of the Constitution are somewhat contradictory and cancel each other out. Adoption of plurality electoral law by India rather than proportional representation also tended to prompt political parties to configure into a two-party system as per the Duverger-Riker ‘iron law’ which stipulates that plurality system inevitably produces a two-party system - on account of this system of representation favouring larger parties at the cost of smaller ones and voters’ psychology of tactical voting  favouring parties more likely to win rather than those likely to lose.