Objection 1. It would seem unfitting to distinguish six kinds of sin against the Holy Ghost, viz. despair, presumption, impenitence, obstinacy, resisting the known truth, envy of our brother's spiritual good, which are assigned by the Master (Sent. ii, D, 43). For to deny God's justice or mercy belongs to unbelief. Now, by despair, a man rejects God's mercy, and by presumption, His justice. Therefore each of these is a kind of unbelief rather than of the sin against the Holy Ghost.
Objection 2. Further, impenitence, seemingly, regards past sins, while obstinacy regards future sins. Now past and future time do not diversify the species of virtues or vices, since it is the same faith whereby we believe that Christ was born, and those of old believed that He would be born. Therefore obstinacy and impenitence should not be reckoned as two species of sin against the Holy Ghost.
Objection 3. Further, "grace and truth came by Jesus Christ" (John 1:17). Therefore it seem that resistance of the known truth, and envy of a brother's spiritual good, belong to blasphemy against the Son rather than against the Holy Ghost.
Objection 4. Further, Bernard says (De Dispens. et Praecept. xi) that "to refuse to obey is to resist the Holy Ghost." Moreover a gloss on Leviticus 10:16, says that "a feigned repentance is a blasphemy against the Holy Ghost." Again, schism is, seemingly, directly opposed to the Holy Ghost by Whom the Church is united together. Therefore it seems that the species of sins against the Holy Ghost are insufficiently enumerated.
On the contrary, Augustine [Fulgentius] (De Fide ad Petrum iii) says that "those who despair of pardon for their sins, or who without merits presume on God's mercy, sin against the Holy Ghost," and (Enchiridion lxxxiii) that "he who dies in a state of obstinacy is guilty of the sin against the Holy Ghost," and (De Verb. Dom., Serm. lxxi) that "impenitence is a sin against the Holy Ghost," and (De Serm. Dom. in Monte xxii), that "to resist fraternal goodness with the brands of envy is to sin against the Holy Ghost," and in his book De unico Baptismo (De Bap. contra Donat. vi, 35) he says that "a man who spurns the truth, is either envious of his brethren to whom the truth is revealed, or ungrateful to God, by Whose inspiration the Church is taught," and therefore, seemingly, sins against the Holy Ghost.
I answer that, The above species are fittingly assigned to the sin against the Holy Ghost taken in the third sense, because they are distinguished in respect of the removal of contempt of those things whereby a man can be prevented from sinning through choice. These things are either on the part of God's judgment, or on the part of His gifts, or on the part of sin. For, by consideration of the Divine judgment, wherein justice is accompanied with mercy, man is hindered from sinning through choice, both by hope, arising from the consideration of the mercy that pardons sins and rewards good deeds, which hope is removed by "despair"; and by fear, arising from the consideration of the Divine justice that punishes sins, which fear is removed by "presumption," when, namely, a man presumes that he can obtain glory without merits, or pardon without repentance.
God's gifts whereby we are withdrawn from sin, are two: one is the acknowledgment of the truth, against which there is the "resistance of the known truth," when, namely, a man resists the truth which he has acknowledged, in order to sin more freely: while the other is the assistance of inward grace, against which there is "envy of a brother's spiritual good," when, namely, a man is envious not only of his brother's person, but also of the increase of Divine grace in the world.
On the part of sin, there are two things which may withdraw man therefrom: one is the inordinateness and shamefulness of the act, the consideration of which is wont to arouse man to repentance for the sin he has committed, and against this there is "impenitence," not as denoting permanence in sin until death, in which sense it was taken above (for thus it would not be a special sin, but a circumstance of sin), but as denoting the purpose of not repenting. The other thing is the smallness or brevity of the good which is sought in sin, according to Romans 6:21: "What fruit had you therefore then in those things, of which you are now ashamed?" The consideration of this is wont to prevent man's will from being hardened in sin, and this is removed by "obstinacy," whereby man hardens his purpose by clinging to sin. Of these two it is written (Jeremiah 8:6): "There is none that doth penance for his sin, saying: What have I done?" as regards the first; and, "They are all turned to their own course, as a horse rushing to the battle," as regards the second.
Reply to Objection 1. The sins of despair and presumption consist, not in disbelieving in God's justice and mercy, but in contemning them.
Reply to Objection 2. Obstinacy and impenitence differ not only in respect of past and future time, but also in respect of certain formal aspects by reason of the diverse consideration of those things which may be considered in sin, as explained above.
Reply to Objection 3. Grace and truth were the work of Christ through the gifts of the Holy Ghost which He gave to men.
Reply to Objection 4. To refuse to obey belongs to obstinacy, while a feigned repentance belongs to impenitence, and schism to the envy of a brother's spiritual good, whereby the members of the Church are united together.
Source: Summa Theologica (New Advent)