Dredge

[Maxpayne03]

if I have {Sylvan Library} On the battlefield and I replace all the draws with dredge, can I put two of the dredge cards back? If not, what would happen if I am left with only 4 life?

[blabla]

Dredge says if you would draw, you may dradge instead. So if you sylvan libraried, you canmt pur the drawn card back since there are none. So, you dredge as a replacement ability, and sylvan library says put two cards back. So i think you put the other drawn without dredge? Correct me if im wrong

[Remillo]

If you replace all of the draws with Dredge, you won't have to pay life, since no cards can be chosen.  If you only replace one or two, you'll have to pay life for the one or two you've drawn.  Basically, if there are cards to choose (that you've drawn that turn), you have to choose them and pay or put them back.  If none can be chosen, since you replaced all the draws, you're in the clear.

Relevant Gatherer Ruling:
9/16/2007: If you choose to draw two cards, then replace one or more of those draws with some other effect, the rest of Sylvan Library's ability still happens. If you've actually drawn only one card that turn, you must choose that card and either pay 4 life or put it on top of your library. If you haven't actually drawn any cards that turn, the rest of the ability has no effect.