Commentary for Avodah Zarah 105:19

The Talmud now offers a different context for R. Hillel’s statement. Obviously, a Jew cannot annul the idol of a non-Jew. Why would the Mishnah need to state this? The answer is that the idol was owned jointly by both parties. The Mishnah teaches that while the Jew cannot annul the part owned by the non-Jew (this is obvious) the non-Jew can still annul his own part in the joint ownership.

This is yet another setting for R. Hillel’s statement. R. Shimon b. Menasya holds that an idol belonging to an Israelite can never be annulled. R. Hillel adds that this is so even if he owns it jointly with a non-Jew. The Jew worships on the idol on his own account and even if the idolater annuls it, the idol is still prohibited.

In order to annul an idol, the idolater must treat the idol with enough disrespect that we can be confident that the idol is no longer considered to be holy by the non-Jew. Note, that the issue is not a physical issue. The mishnah is not asking the question, does this still look like an idol. Rather the issue is psychological. At what point can an outside observer assume that the owner of the idol no longer is relating to it as a god, but rather as merely a physical item devoid of religious meaning.
The first way for the owner to annul the idol is to somehow physically damage it. If he cuts off one of its appendages, this is sufficient physical damage for it to be annulled. Furthermore, if he defaces, meaning he distorts the facial features of the idol, it is annulled, even if he has not diminished the material used to make the idol.

Acting in a disgraceful way in front of the idol does not annul it.

If a non-Jew sells or uses the idol as a pledge, according to Rabbi [Judah the Prince] he has annulled the idol. Since he treated it in a profane matter, and did something that one would not do to a divine idol, he must no longer be considering it to be an idol. The other Sages disagree with Rabbi.

As I basically explained above, since he defaced the idol it is annulled, even though he didn’t actually break anything off of it.

The verse here describes an idolater who curses his king and god, and then looks upward to the true God. Nevertheless, he immediately looks down to the earth, which Hezekiah reads as continuing his idolatry. Thus even though the idolater shows his anger at his idol, he has not really annulled it, even if he spits or urinates on it.

The amoraim discuss a case where the idol was sold to a smelter. According to one opinion, the tannaim disagree if it was sold to an idolatrous smelter. One tanna hold that since the smelter is idolatrous, he might use the metal to make another idol. But if he sold it to an Israelite, the Israelite will surely melt it down for another purpose, and thus this is annulment. While the other tanna holds that even selling it to an idolater is considered annulment.
The other amora thinks that the tannaim disagree when sold to an Israelite smelter.

Above we said that according to one amora, the tannaim disagree over a case where the idol was sold to an Israelite smelter. The question is whether according to this amoraic opinion the tannaim also disagree over a case where it was sold to an idolatrous smelter. Or do they agree that when he sells it to an idolatrous smelter, it is not annulled.
To answer this, the Talmud looks at a baraita. In this baraita Rabbi says that his opinion is correct if the idolater sells it to one who plans on destroying the idol, but that the sages’ opinion is correct when he sells it to one who will worship it, which here is interpreted to be an idolatrous smelter. Rabbi’s words imply that there is a dispute in both cases. In other words, although Rabbi says that his colleagues’ opinion seems correct, he still disagrees.

We now reinterpret the baraita. Rabbi does not say that his colleagues simply agree with him about a case where it was sold to be destroyed. They never differed in the first place. The only disagreement is whether it is annulled when it was sold to another idolater.

The baraita discusses a Jew who buys scrap metal from a non-Jew and finds an idol in there. This is a case of selling the idol to be destroyed. The baraita itself says that if he only took it into his possession, he can return the idol and simply not pay for it. But if he also paid for it, he cannot get his money back.
But this baraita makes sense only if the sages in the mishanh also disagree when he sold it to a Jew to be destroyed. This baraita would follow the opinion of the rabbis. But if all agree that when he sold it to a Jew it was annulled, then why shouldn’t the Jew just keep it under all circumstances?

If he sold the metal thinking that it was scrap metal, then he has not annulled it. He did not even know he was selling an idol, so how could he have annulled it. The rabbis and Rabbi Judah Hanasi disagree only in a case where he knew he was selling an idol to a Jewish smelter who would certainly destroy it.

In all of these scenarios, the owner hopes to recover his idol and therefore has not annulled it in his heart.
According to the rabbis, when the Canaanites fled when Joshua was conquering the land they intended to return. Therefore, they were not really abandoning their idols.