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.
Jewish views on sin
The generic Hebrew word for any kind of sin is "avera" (literally: transgression). Based on verses in the Hebrew Bible, Judaism describes three levels of sin. There are three categories of a person who commits an avera. The first one is someone who does an avera intentionally, or "B'mezid." This is the most serious category. The second is one who did an avera by accident. This is called "B'shogeg," and while the person is still responsible for their action it is considered less serious. The third category is someone who is a "Tinok Shenishba", which is a person who was raised in an environment that was assimilated or non-Jewish, and is not aware of the proper Jewish laws, or halacha. This person is not held accountable for his or her actions.