Eternal sin
Thomas Aquinas lists, or has responded to, six sins that supposedly go against the Holy Spirit:
Thomas Aquinas explains that the unforgivability of blasphemy against the Holy Spirit means that it removes the entrance to these means of salvation; however, it cannot hinder God in taking away this obstacle by way of a miracle.
Tawhid
Greater Shirk consists of the above-mentioned deeds. A person commits lesser shirk (Shirk-al-Asghar) or hidden polytheism when he claims to believe in God but his thoughts and actions do not reflect his belief. There are also minor forms of Shirk, they must be avoided as well; these include committing a good deed to show off, making an oath in the name of anyone except God. Within Islam, shirk is an unforgivable crime; God may forgive any sin if one dies in that state except for committing shirk, repentance is required for its forgiveness.