the transaction. In the development of his idea, Tobin was influenced by the earlier work of John Maynard Keynes on general financial transaction taxes. Keynes' concept stems from 1936 when he proposed that a transaction tax should be levied on dealings on Wall Street, where he argued that excessive speculation by uninformed financial traders increased volatility. For Keynes (who was himself a speculator) the key issue was the proportion of 'speculators' in the market, and his concern that, if left unchecked, these types of players would become too dominant. Variations on Tobin tax idea The most common variations on Tobin's idea are a general currency transaction tax, a more general financial transaction tax and (the most general) Robin Hood tax on transactions only richer investors can afford to engage in. Pollin and Baker A key issue with Tobin's tax was "avoidance by change of product mix... market participants would have an incentive to substitute out of financial instruments subject to the tax and into instruments not subject to it. In this fashion, markets would innovate so as to avoid the tax... [so] focusing on just spot currency markets would clearly induce a huge shifting of transactions into futures and derivatives markets. Thus, the real issue is how to design a tax that takes account of all the methods and margins of substitution that investors have for changing their patterns of activity to avoid the tax. Taking account of these considerations implies a Tobin tax that is bigger in scope, and pushes the design toward a generalized securities transaction tax that resembles the tax suggested by Pollin et al. (1999). There are four benefits to this. First, it is likely to generate significantly greater revenues. Second, it maintains a level playing field across financial markets so that no individual financial instrument is arbitrarily put at a competitive disadvantage versus another. Third, it is likely to enhance domestic financial market stability by discouraging domestic asset speculation. Fourth, to the extent that advanced economies already put too many real resources into financial dealings, it would cut back on this resource use, freeing these resources for other productive uses [Fourth] such substitution is costly both in resource use, and because alternative instruments do not provide exactly the same services [thus] just as the market provides an incentive to avoid a Tobin tax, so too it automatically sets in motion forces that deter excessive avoidance."