MTVMultiplayer: "In the world of "BioShock Infinite," vigors are like your spells. In practice, they work a lot like plasmids in the sense that you can drink a vigor and send out burst of ravenous crows (Murder of Crows) or lift enemies up into the air (Bucking Bronco). Until I spoke to Levine, I assumed that they worked exactly like plasmids, where the player would select which vigors they wanted and would have a pool of energy (or Eve, in "BioShock 1") which would allow them to be cast.
"The big difference we're doing is that vigors have, essentially, charges," explained Levine. "One problem we had with Eve is that all the plasmids had to be roughly equally as powerful as all the other plasmids because they all ran from the same Eve system. You basically felt like 'Well, if I fire this plasmid versus that plasmid, I can only get one round, where here I can get 50 rounds, but it's much less powerful.'"