In the beginning of Edgar Allan Poe's story, "The Cask of Amontillado," Montresor proposes a three-part definition of revenge:
1. The avenger must punish with impunity.
2. Retribution must not overtake its redresser.
3. The avenger must make himself known to the one he punishes.
Certainly, the first part is fulfilled as Montresor boasts that it has been fifty years since his crime, and no one has "disturbed" the masonry that he has laid, enclosing Fortunato into a catacomb wall. (He has also satisfied his family code of honor which is written on the Montresor coat of arms.)
Regarding the second condition, its fulfillment is questionable since Montresor is still telling this tale "a half century" later, a fact that seems to indicate that he is rather obsessed ("overtaken") with what he has done. His mental disturbance seems evident, too, in the fact that he has neglected to cite either for Fortunato or for the reader any of the "thousand injuries of Fortunato."
That he has made himself known to Fortunato--his third requirement--is also apparent since Fortunato has demonstrated his realization of what was being done to him as he cries, "For the love of God, Montresor." Yet, even with this statement, there is some question as to whether Fortunato knows the reason for Montresor's revenge. (Of course, the reader does not know, either.) So, if making oneself known to the victim implies that the victim have both knowledge of the avenger and his reason for retribution, the third condition has not been fully completed.
Once again, Poe's typically unreliable narrator leaves the reader with ambiguity as he/she may doubt the fulfillment of the second condition and debate the third condition of retribution according to Montesor.
I think there is no question that Montresor got the kind of revenge that he wanted on Fortunato. All we have to do to see that is to look at the criteria he had for a satisfactory revenge. To me, there are two things that he wanted -- he wanted to not get caught taking revenge, and he wanted Fortunato to know what was happening to him. Both of those were clearly accomplished.
As far as we know, no one ever suspected what had happened to Fortunato. And we can clearly see that Fortunato knew what was happening to him and who was doing it.
The question I do have, however, is whether Montresor really enjoyed it as much as he thought he would.
Montresor carefully and very systematically plans his revenge on Fortunato:
1.Time: Montresor decides to take his revenge at "about dusk, one evening during the supreme madness of the carnival season," so that every one in his house especially the servants would have gone out and that he would be able to commit his heinous deed completely unnoticed by anyone. He had cunningly ensured that the servants would not return home that evening by lying to them that he will be returning home only next morning.
2.Place: Montresor chose the innermost crypt in his vaults so that Fortunato's cries would not be heard by anyone. He had also arranged to have the building stones and the mortar ready at hand to wall in Fortunato. When he accompanies Fortunato into the vaults he carries with him the instrument of revenge-the trowel.
3.The Method: All the while "smiling in his face" Montresor flatters and traps Fortunato by exploiting his "weak point" : Fortunato "prided himself on his connoisseurship in wine," and Montresor deceives him by saying that he does not wish to trouble him and that he'd rather seek Luchresi's opinion regarding the quality of the Amontillado that he has bought. At once Fortunato takes the bait and accompanies Montresor into the vaults to prove that he is better than Luchresi. Once inside the vaults, Montresor gets him drunk to slow down his reflelexes and then leads him to his death.Consequently there is no doubt that he achieves the kind of revenge that he wants to take as mentioned in the first paragraph:
the very definitiveness with which it [the act of revenge] was resolved precluded the idea of risk. I must not only punish, but punish with impunity.The word 'impunity' means 'completely unconcerned about being punished.' Montresor remarks at the end of the story,
For the half of a century no mortal has disturbed them.clearly indicating that he has got away with killing Fortunato.