Once upon a time, there was an evil, evil man named Yed who was a notorious poisoner. He was hired as an assassin by many unscrupulous persons but over time each had hired him in turn and had managed to kill one another through his nefarious potions. Once he had no further employment, he took to poisoning his neighbors and townspeople in the area.
Fortunately, these people had long experience with Yed and were wise to his ways. They knew just which antidote to use, and could quickly administer whatever was needed to purge one of Yed's victims of his terrible, noxious toxins. However, this was very frustrating to them and also a waste of their time. The townsfolk had so many other, better things to be doing rather than curing Yed's victims. They became so annoyed with Yed that they assigned the town's most sagacious mage and the strictest cleric to approach Yed about his misdeeds and set him right.
Yed was captured and taken to a special escape-proof room with none of his secret mixtures, and no help for him. These neighbors and townspeople knew just where to catch him at his most vulnerable. For a year and a day, the cleric and the mage took it in turns to reform Yed. They lectured, they scolded, they pleaded, they cajoled, they threatened. Finally, they told him he had a choice: change or die.
After that year and a day, Yed was ashamed at what he had done and repented of his poisoning ways. He agreed to set his life of crime behind and become a changed man. The mage and the cleric were skeptical, but Yed reassured them: "That life was wicked, but all that I, Yed, had known. I will set that life aside and take on a new name, one that is untainted by such evil deeds, and I will be a new person."
The mage and the cleric agreed. They made an announcement to the townsfolk, celebrating the reformation of the poisoner and welcoming him to his new life. "This poisoner is gone and reformed!" they cried aloud to their fellows and neighbors. "We shall purge that name as if it were one of the poisons which so tormented his victims! Never again after this will the name of Yed be allowed! From now on, his name is Ied and in no word or deed shall his former name be remembered." That is why to this day we do not use "Yed" in words, we change the spelling to "Ied."
Ied set aside his poisons, and went into the bomb-making business.
This is the story of Yed. This is how one mom explains to her son why it is to this day that when a word ends in Y, that letter must be changed to I before adding ed. This is the story that helped my son ace his 3rd grade spelling test, with words including carried, applied, tried.
More reading on suffix rule induction and morpohology is available from the folks at OKstate.edu.
Photo credit to Grumbler %-|.