Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that all sins are due to the temptation of the devil. For Dionysius says (Div. Nom. iv) that "the multitude of demons is the cause of all evils, both to themselves and to others." And Damascene says (De Fide Orth. ii, 4) that "all malice and all uncleanness have been devised by the devil."

Objection 2: Further, of every sinner can be said what the Lord said of the Jews (Jn. 8:44): "You are of your father the devil." But this was in as far as they sinned through the devil's instigation. Therefore every sin is due to the devil's instigation.

Objection 3: Further, as angels are deputed to guard men, so demons are deputed to assail men. But every good thing we do is due to the suggestion of the good angels: because the Divine gifts are borne to us by the angels. Therefore all the evil we do, is due to the instigation of the devil.

On the contrary, It is written (De Eccl. Dogmat. xlix): "Not all our evil thoughts are stirred up by the devil, but sometimes they arise from the movement of our free-will."

I answer that, One thing can be the cause of another in two ways; directly and indirectly. Indirectly as when an agent is the cause of a disposition to a certain effect, it is said to be the occasional and indirect cause of that effect: for instance, we might say that he who dries the wood is the cause of the wood burning. In this way we must admit that the devil is the cause of all our sins; because he it was who instigated the first man to sin, from whose sin there resulted a proneness to sin in the whole human race: and in this sense we must take the words of Damascene and Dionysius.

But a thing is said to be the direct cause of something, when its action tends directly thereunto. And in this way the devil is not the cause of every sin: for all sins are not committed at the devil's instigation, but some are due to the free-will and the corruption of the flesh. For, as Origen says (Peri Archon iii), even if there were no devil, men would have the desire for food and love and such like pleasures; with regard to which many disorders may arise unless those desires are curbed by reason, especially if we presuppose the corruption of our natures. Now it is in the power of the free-will to curb this appetite and keep it in order. Consequently there is no need for all sins to be due to the instigation of the devil. But those sins which are due thereto man perpetrates "through being deceived by the same blandishments as were our first parents," as Isidore says (De Summo Bono ii).

Thus the answer to the first objection is clear.

Reply to Objection 2: When man commits sin without being thereto instigated by the devil, he nevertheless becomes a child of the devil thereby, in so far as he imitates him who was the first to sin.

Reply to Objection 3: Man can of his own accord fall into sin: but he cannot advance in merit without the Divine assistance, which is borne to man by the ministry of the angels. For this reason the angels take part in all our good works: whereas all our sins are not due to the demons' instigation. Nevertheless there is no kind of sin which is not sometimes due to the demons' suggestion.

Articulus 3

Argumentum 1

Ad tertium sic proceditur. Videtur quod omnia peccata procedant ex tentatione diaboli.

Dicit enim dionysius, IV cap. De div. Nom., quod multitudo Daemonum est causa omnium malorum et sibi et aliis.

Et Damascenus dicit quod omnis malitia et omnis immunditia a diabolo excogitatae sunt.

Argumentum 2

Praeterea, de quolibet peccatore dici posset quod dominus de Iudaeis dicit, Ioan. VIII, vos ex patre diabolo estis.

Hoc autem est inquantum ipsi ex diaboli suggestione peccabant.

Omne ergo peccatum est ex suggestione diaboli.

Argumentum 3

Praeterea, sicut Angeli deputantur ad custodiam hominum, ita Daemones ad impugnationem. Sed omnia bona quae facimus, ex suggestione bonorum Angelorum procedunt, quia divina ad nos mediantibus Angelis perferuntur. Ergo et omnia mala quae facimus, proveniunt ex suggestione diaboli.

Sed Contra

Sed contra est quod dicitur in libro de eccles. Dogmat., non omnes cogitationes nostrae malae a diabolo excitantur, sed aliquoties ex nostri arbitrii motu emergunt.

Corpus

Respondeo dicendum quod causa alicuius potest dici aliquid dupliciter, uno modo, directe, alio modo, indirecte. Indirecte quidem, sicut cum aliquod agens causans aliquam dispositionem ad aliquem effectum, dicitur esse occasionaliter et indirecte causa illius effectus; sicut si dicatur quod ille qui siccat ligna, est causa combustionis eorum. Et hoc modo dicendum est quod diabolus est causa omnium peccatorum nostrorum, quia ipse instigavit primum hominem ad peccandum, ex cuius peccato consecuta est in toto genere humano quaedam pronitas ad omnia peccata.

Et per hunc modum intelligenda sunt verba Damasceni et dionysii.

Directe autem dicitur esse aliquid causa alicuius, quod operatur directe ad illud. Et hoc modo diabolus non est causa omnis peccati non enim omnia peccata committuntur diabolo instigante, sed quaedam ex libertate arbitrii et carnis corruptione. Quia, ut Origenes dicit, etiam si diabolus non esset, homines haberent appetitum ciborum et venereorum et huiusmodi; circa quae multa inordinatio contingit, nisi per rationem talis appetitus refraenetur; et maxime, supposita corruptione naturae. Refraenare autem et ordinare huiusmodi appetitum, subiacet libero arbitrio.

Sic ergo non est necessarium omnia peccata ex instinctu diaboli provenire. Si qua tamen ex instinctu eius proveniunt, ad ea complenda eo blandimento decipiuntur homines nunc, quo primi parentes, ut Isidorus dicit.

Ad 1

Et per hoc patet responsio ad primum.

Ad 2

Ad secundum dicendum quod, si qua peccata absque instinctu diaboli perpetrantur, per ea tamen fiunt homines filii diaboli, inquantum ipsum primo peccantem imitantur.

Ad 3

Ad tertium dicendum quod homo potest per seipsum ruere in peccatum, sed ad meritum proficere non potest nisi auxilio divino, quod homini exhibetur mediante ministerio Angelorum.

Et ideo ad omnia bona nostra cooperantur Angeli, non tamen omnia nostra peccata procedunt ex Daemonum suggestione.

Quamvis nullum genus peccati sit, quod non interdum ex Daemonum suggestione proveniat.