can federer defeat nadal in a clay court??

This is really a tough one. But I think by the way Federer is improving in clay court he'll be a French Open Champion someday..... We also saw him defeat Nadal in Rome before the French Open.. So there is chance for Federer to beat Nadal at Roland Garros......

It is definitely possible and i think thats wat going to happen in the French Open this year.

Yes, it is definitely possible.Federrer has to motivate himself to another level and remind that this is the same guy whom he is used to defeating on the grass courts.I think Nadal moves faster on clay courts than Federrer does and that edge assists him to win.If federrer can find a way to match his mobility on a clay court,he will win.

it is tough but, i think nothing is impossible, in game you are not able to decide any thing until laste moment comes and refery declares the winner, so i think in game luckyness palys a big role, so have patience , and follow the chain

No I don't think he can. A lot of great palyers over the years have had their tournaments or surfaces that they have struggled on. I truely believe the Federer will never win the French Open. He is good on clay but Nadal is better. Federer will go down as one of the greatest ever players, just without a French Open title.