Avodah Zarah, Chapter Four, Mishnah Four
The first part of mishnah four discusses when an idol becomes prohibited from being used by a Jew. The second half of the mishnah discusses when an idol that was once worshipped becomes annulled as an idol and thereby permitted to be used by a Jew. Note that we already discussed the process of annulling an idol in the last mishnah of chapter three.
1) The idol of an idolater is prohibited immediately;
a) but if it belonged to a Jew it is not prohibited until it is worshipped.
2) An idolater can annul an idol belonging to himself or to another idolater,
a) but a Jew cannot annul the idol of an idolater.
3) He who annuls an idol annuls the things that pertain to it.
a) If he only annulled the things that pertain to it these are permitted but the idol itself is prohibited.
Section one: As soon as an idol is made by a non-Jew it is prohibited, even before it is worshipped. The reason is that we can safely assume that the non-Jew will worship the idol, and it was certainly made for idolatrous purposes. However, an idol made by a Jew is only forbidden for Jewish use once it has been worshipped. The reason is that we cannot be sure that the Jew will worship the idol. It potentially could be used for decorative, non-idolatrous purposes.
Section two: One who is engaged in idolatry can annul an idol that belongs to him and one that belongs to others. We will learn in the proceeding mishnayoth how one annuls idols. However, a Jew cannot annul the idol of an idolater.
Section three: If one annuls an idol, all of the things that go with the idol, for instances the plates used to make offerings to it, are also annulled. Since these things are ancillary to the main idol, they are effected by its change of status. However, if one annuls the things that pertain to the idol, without specifically annulling the idol, the idol is still forbidden.