"To be disfellowshipped, an apostate does not have to be a promoter of apostate views....If a baptized Christian abandons the teachings of Jehovah, as presented by the faithful and discreet slave, and persists in believing other doctrine despite Scriptural reproof, then he is apostasizing. Extended, kindly efforts should be put forth to readjust his thinking. However, if, after such extended efforts have been put forth to readjust his thinking, he continues to believe the apostate ideas and rejects what he has been provided through the 'slave class', then appropriate judicial action should be taken." (Letter to all Circuit and District Overseers, 9/1/80).
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BY definition, any thoughts that do not agree 100% with the GB/WT/ "faithful slave" constitute "apostasy" and can lead to DF. In practice, this happens when a JW questions the legitimacy/authority of the GB or questions a WT doctrine.
Note in the above letter excerpt a JW can be convicted for thought crime, not for actually promoting a differing view.
Note: "apostasy", according to WT's definition, is disagreeing with WT on any subject.
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*** jv chap. 28 p. 629 Testing and Sifting From Within. From 2009 CD Rom
"But anyone who publicly or privately advocates views that are divergent from what appears in the publications of an organization, and who does so while claiming to represent that organization, causes division."
*** w86 4/1 pp. 30-31 Questions From Readers ***
Questions From Readers
Why have Jehovah’s Witnesses disfellowshipped (excommunicated) for apostasy some who still profess belief in God, the Bible, and Jesus Christ?
....Approved association with Jehovah’s Witnesses requires accepting the entire range of the true teachings of the Bible, including those Scriptural beliefs that are unique to Jehovah’s Witnesses. What do such beliefs include?
... Following such Scriptural patterns, if a Christian (who claims belief in God, the Bible, and Jesus) unrepentantly promotes false teachings, it may be necessary for him to be expelled from the congregation."
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"false teachings" are any teachings not taught by the WT.