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.
Catholic theology of sexuality
The Catholic Church disapproves of masturbation. Thomas Aquinas, one of the most prominent Doctors of the Catholic Church, wrote that masturbation was an "unnatural vice" which is a species of lust", but that it is a less serious form than bestiality, which is "the most serious", and than sodomy, which is the next most serious: "By procuring pollution [i.e., ejaculation apart from intercourse], without any copulation, for the sake of venereal pleasure [...] pertains to the sin of 'uncleanness' which some call 'effeminacy' [Latin: "mollitiem", lit. 'softness, unmanliness']."