The most intriguing aspect of the monsoon session of Parliament that got under way this week will not be the debates or the bills or the antics of MPs throwing tantrums. It is who is the real opposition - the communists or the Bharatiya Janata Party? It seems a curious question. Surely it's the BJP, the second-largest party in Parliament after the ruling Congress party. BJP president Lal Krishna Advani is, after all, the formal leader of the opposition. But over the past year, since Congress formed a coalition government that includes the two communist parties, it is the communists who have been acting as the de facto opposition. Stranger still, the communists are not members of the government but the support of their 62 MPs is crucial to the Congress-led coalition's survival. Whatever the policies pursued by Congress - the recent nuclear pact with the US, phasing out subsidies on basic commodities, oil price rises, privatisation of state-owned companies - it is the communists who have relentlessly attacked the government. 'It's crucial for the left to be seen to be critical of the Congress because, while it's happy keeping the BJP out of power, it doesn't want to alienate its traditional supporters by appearing soft on the Congress,' political analyst Neerja Chowdhury said. If the left has seized the ground that should be occupied by the BJP, the BJP has only itself to blame. First, the soul-searching after its shock defeat in the general election last year dragged on, rendering it useless. Then, in a fit of petulance, the party boycotted the last session of Parliament. Now it is immersed in a vicious internal battle over Mr Advani's future as leader. In this session, the party will be watched closely to see whether it can act as a responsible and effective opposition. The signs are not too promising so far. 'Advani really has to prove himself, and it's going to be difficult because the turbulence in his party continues to rage,' columnist Inder Malhotra said.