What was the main difference between the mensheviks and the bolsheviks?

The differences between the Bolsheviks and the Mensheviks derived from different opinions on the role of the party and the nature of revolution.

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The Mensheviks (sometimes called Menshevists Russian: меньшевик) were a faction of the Russian socialist movement that emerged in 1904 after a dispute in the Russian Social-Democratic Labour Party between Vladimir Lenin and Julius Martov, leading to the party splitting into two factions, one being the Mensheviks and the other being the Bolsheviks. The dispute originated at the Second Congress of the RSDLP, ostensibly over minor issues of party organization. Martov's supporters, who were in the minority in a crucial vote on the question of party membership, came to be called Mensheviks, derived from the Russian word меньшинство (minority), whereas Lenin's adherents were known as Bolsheviks, from большинство (majority).
 Neither side held a consistent majority over the course of the congress. The split proved to be long-standing and had to do both with pragmatic issues based in history, such as the failed revolution of 1905, and theoretical issues of class leadership, class alliances, and interpretations of historical materialism. While both factions believed that a "bourgeois democratic" revolution was necessary, the Mensheviks generally tended to be more moderate and were more positive towards the liberal opposition and the dominant peasant-based Socialist Revolutionary party.