This epigraph is taken from Dante's Divine Comedy. It reads: "If I thought my answer were to one who could ever return to the world, this flame would move no more; but since no one has ever returned alive from this depth, if what I hear be true, without fear of infamy I answer you." The words are spoken by a lost soul, damned to Hell for the attempt to buy absolution in advance of committing a crime. This correlates with Prufrock's need to know the answer to the question he wants to ask as a condition of asking it. Or perhaps in order for Prufrock to be able to ask the question he would have to not care what the answer would be; in that case, the answer wouldn't matter.
