imO discounting is all about hedging: [1] For negative future CFs you should ask yourself: What is the least amount of money that I need to invest today to receive 1$ in T (without taking on any credit risk!) [2] For positive future CFs you should ask yourself: What is the highest amount I can borrow with a promise to pay back 1$ in TFor [2] it is obviously the funding rate and actually for [1] as well, because - From the view of the trader the treasury desk is risk free (if the bank goes bankrupt it does not matter anyway) - The trader will not a find a different (almost) risk-free source that pays him a higher rate as treasuryHere I obviously assume that treasury offers the trader zero-bond investments for whatever horizon he asks for ...So why use OIS for collateralized trades then. Actually a collateralized trade is a portfolio of the payoff specified by the trade and the stochastic flows from the collateral account. Both parts of the portfolio should be discounted with the funding rate, which results in quiet a nasty valuation formula. Luckily for us, it turns out the this valuation formula is exactly the same as discounting the payoff specified by the trade on the OIS curve (i.e. OIS discounting is just a theoretical shortcut). However, the premise is of course that you can invest on the OIS curve, i.e. bootstrapping zero-bonds form the tradeable ois swaps. I have asked myself this questions a few times before but never had the time to really work it out. Does anybody have a solution to this?I want to add one last thing: OIS is NOT the correct discount rate because it is risk-free but simply because it is the typical rate specified in the CSAs (OIS is probably the closest thing you will find to risk free but this simply does not matter here). If the CSAs would use some Greek bond rate to determine the yield on the collateral account then this would be the correct discount rate.Would be happy to discuss

.Cheers,Bernd