Three lectures (1369, 1370, 1375), and it is Neville's narrowest and most aggressive definition: there is no sin against the Holy Ghost other than man's belief that something is impossible to his own wonderful human imagination. The traditional unforgivable sin is emptied of its content and refilled with one attitude, and the argument for it is an argument from the man's own existence rather than from scripture. You are here and you do not know how or why; you were physically born by the grace of God and cannot make one hair on your head or one fingernail grow; so when you dare to put a limit on the power that brought you here, you are contradicting the only thing you know for certain about it. The consequence is drawn with the word tag at 1370, which is the sharpest form: he gives to some state that tag, it's impossible, and therefore he sins against the Holy Ghost. So the sin is not blasphemy, not despair and not unbelief in a doctrine - it is a judgement passed on a particular desire, and it is committed silently by people who think they are being realistic. It never appears without the Shaw quotation that sets it up (M1109).
CORRECTION, 2026-09-20. The first version of this record named five lectures, adding 1081 and 1851. The attach lane checked both and they are a different reading of the same phrase: in each, the sin against the Holy Ghost is failing to confess when supernaturally prompted (Luke 12:11-12), which is M764. They are correctly kept off this motif, and the count here is three.