The idiom “apple of discord” refers to anything that causes dispute or contention. When someone “throws in an apple of discord” they are doing something that causes disagreement or strife among individuals in a group. Basically, then, an apple of discord is anything that causes trouble among people. The expression usually has the connotation of being deliberate.
It would seem obvious that this expression must come from the biblical story of Adam and Eve. In the story, God had ordered them never to eat the fruit of the tree of knowledge of good and evil. This fruit is usually referred to as an apple, but it almost certainly was not an apple as we know it.
This fruit, or apple, definitely ends up causing a lot of discord. Adam and Eve do not die from it, but they lose their Biblical paradise, meaning, of course, that mankind lost paradise. The apple is, in fact, why the lump in men’s throats is called the Adam’s apple.
Yet, this is not the source of the expression apple of discord. Instead, it comes from Greek and Roman mythology. The story of the Apple of Discord is connected to the Trojan war, at least according to Homer and some other late sources.
It all starts when Eris, the Goddess of discord, hardship, and strife (called Discordia by the Romans) is not invited to the wedding of Peleus and Thetis, who are the parents of Achilles. If you know anything about Eris, you will see why nobody wanted her at the wedding.
The sister of Ares (Mars) the God of War, Eris is a malevolent deity who lives only to cause trouble and bring about destruction. Her children are equally terrible: Algea or Pain, Amphilligoiai or Disputes, Androctasiai or Mansaughters, Ate or Ruin, Dysnomia or Anarchy, Horkos or Oath (punisher of men who utter false oaths), Hysminia or Fighting, Makhai or Battles, Neika or Disagreement, Ponos or Work and Toil, Limos or Famine, Lethe or Forgetfullness, Phonoi or Massacres, and Psuedia or Lies.
Angered at being shunned from the wedding of Peleus and Thetis, she tosses a golden apple into the celebration. It lands right among Aphrodite, Hera, and Athena. There is an inscription on the apple which reads Kallisti meaning “For the Fairest.” Since it seems the apple must be meant the most beautiful among them, they argue about who should get the apple.
At first, Zeus is asked to choose who receives the apple, but Zeus, who was wise enough not to invite Eris to the wedding in the first place, was also wise enough not to get involved in this particular dispute.
Instead, Zeus sends them to Paris ask Paris, the son of Priam the King of Troy, who is the fellow who will later wound Achilles in the heel with an arrow. At this time, however, Paris was up on Mt. Ida having been taken there by Agelaus, the herdsman of Priam. It had been foretold that Paris, when born, would bring about the destruction of Troy and that he should be killed. Neither Priam or Paris’ mother Hecuba could bring themselves to do kill their child. Priam, instead, had asked the chief herdsman Agelaus to take Paris away and kill him.
Agelaus was no more able to kill an infant that the parents, so he had instead taken him up onto Mount Ida and left him there alone, hoping he would die. Instead, he was sucked by a bear and Aegelaus returned more than a week later to find the child, miraculously, still alive. He took the Paris home to raise as his own.
Paris, of course, has his own story but the most relevant question here is why Zeus chose him to be the judge. The reason was that he had earned a reputation among the Gods for being fair-minded and honest. Paris had been having one of Agelaus’ prize bulls engage in fights with other bulls, and the bull had defeated every bull set against him. Paris, then, offered a golden crown (how did this guy get a golden crown?) to anyone with a bull who could defeat his champion. Ares, the aforementioned God of War, transformed himself into a bull and then defeated Paris’ bull with no trouble at all.
Obviously, Ares had cheated, being a God and not a bull, but Paris still gave him the golden crown with no hesitation. This is why Zeus thought he was fair-minded enough to judge honestly which Goddess should get the apple.
Hermes took the three to Paris, who was herding his cattle on Mount Ida, first taking a pit-stop at the spring to bathe. They appeared naked before Paris (whose idea this was is not clear).
They are all exceedingly hot, so Paris has trouble deciding. Each of the three goddesses offer Paris a bribe for choosing them. Hera offers him power and authority, Athena offers him victory in Battle against Athena, and Aphrodite offers him the hand of the most beautiful (mortal) woman in the world in marriage.
Warm-blooded male that he was, Paris chose Aphrodite to get the golden apple, in what became known as the ‘Judgement of Paris.’
The most beautiful woman in the world turned out to be Helen. The trouble was, Helen was already married. In fact, she was married to a Menelaus, who was the King of Sparta! She was known as Helen of Sparta but you may know her as Helen of Troy. Paris had also, of course, infuriated Athena and Hera.
Paris, eager to receive his prize, goes to Sparta while the kind is away, and carries Helen off to Troy with him. It is pretty easy to guess what happened then: a lot of death and destruction. The Greeks combine all their military force to go to war against Troy and bring Helen back, and Troy was destroyed and Achilles, son of the bride and groom, is slain. This is why the golden apple of Eris was called the Apple of Discord. Although Zeus may seem to have washed his hands of the affair by refusing to be the judge, but Homer, for some reason or other, states that the war fulfilled the will of Zeus, perhaps because Zeus wanted to lessen the burden on the Earth, which was over-run by mortals, or because he wanted certain participants to receive glory or both.