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Aquinas, Summa Contra Gentiles, Book I


Book I, Chapter 01. In What Consists the Office of a Wise Man

My mouth shall meditate truth, and my lips shall hate wickedness. (Proverbs 8:7)

The general use which, in the Philosopher’s opinion, should be followed in naming things, has resulted in those men being called wise who direct things themselves and govern them well. Wherefore among other things which men conceive of the wise man, the Philosopher reckons that it belongs to the wise man to direct things. Now the rule of all things directed to the end of government and order must needs be taken from their end: for then is a thing best disposed when it is fittingly directed to its end, since the end of everything is its good. Wherefore in the arts we observe that the art which governs and rules another is the one to which the latter’s end belongs: thus the medical art rules and directs the art of the druggist, because health which is the object of medicine is the end of all drugs which are made up by the druggist’s art. The same may be observed in the art of sailing in relation to the art of ship-building, and in the military art in relation to the equestrian art and all warlike appliances. These arts which govern others are called master-arts (architectonicæ), that is principal arts, for which reason their craftsmen, who are called master-craftsmen (architectores), are awarded the name of wise men. Since, however, these same craftsmen, through being occupied with the ends of certain singular things, do not attain to the universal end of all things, they are called wise about this or that, in which sense it is said (1 Cor. 3:10): As a wise architect, I have laid the foundation; whereas the name of being wise simply is reserved to him alone whose consideration is about the end of the universe, which end is also the beginning of the universe: wherefore, according to the Philosopher, it belongs to the wise man to consider the highest causes.

Now the last end of each thing is that which is intended by the first author or mover of that thing: and the first author and mover of the universe is an intellect, as we shall prove further on. Consequently the last end of the universe must be the good of the intellect: and this is truth. Therefore truth must be the last end of the whole universe; and the consideration thereof must be the chief occupation of wisdom. And for this reason divine Wisdom, clothed in flesh, declares that He came into the world to make known the truth, saying (Jo. 18:37): For this was I born, and for this cause came I into the world, that I should give testimony to the truth. Moreover the Philosopher defines the First Philosophy as being the knowledge of truth, not of any truth, but of that truth which is the source of all truth, of that, namely, which relates to the first principle of being of all things; wherefore its truth is the principle of all truth, since the disposition of things is the same in truth as in being.

Now it belongs to the same thing to pursue one contrary and to remove the other: thus medicine which effects health, removes sickness. Hence, just as it belongs to a wise man to meditate and disseminate truth, especially about the first principle, so does it belong to him to refute contrary falsehood.

Wherefore the twofold office of the wise man is fittingly declared from the mouth of Wisdom, in the words above quoted; namely, to meditate and publish the divine truth, which antonomastically is the truth, as signified by the words, My mouth shall meditate truth; and to refute the error contrary to truth, as signified by the words, and my lips shall hate wickedness, by which is denoted falsehood opposed to divine truth, which falsehood is contrary to religion that is also called godliness, wherefore the falsehood that is contrary thereto receives the name of ungodliness.


Book I, Chapter 02. The Author’s Intention in This Work

Now of all human pursuits, that of wisdom is the most perfect, the most sublime, the most profitable, the most delightful. It is the most perfect, since in proportion as a man devotes himself to the pursuit of wisdom, so much does he already share in true happiness: wherefore the wise man says (Ecclus. 14:22): Blessed is the man that shall continue in wisdom. It is the most sublime because thereby especially does man approach to a likeness to God, Who made all things in wisdom: wherefore since likeness is the cause of love, the pursuit of wisdom especially unites man to God by friendship: hence it is said (Wis. 7:14) that wisdom is an infinite treasure to men: which they that use, become the friends of God. It is the most profitable, because by wisdom itself man is brought to the kingdom of immortality, for the desire of wisdom bringeth to the everlasting kingdom (Wis. 6:21). And it is the most delightful because her conversation hath no bitterness, nor her company any tediousness, but joy and gladness (Wis. 8:16).

Wherefore, taking heart from God’s lovingkindness to assume the office of a wise man, although it surpasses our own powers, the purpose we have in view is, in our own weak way, to declare the truth which the Catholic faith professes, while weeding out contrary errors; for, in the words of Hilary, I acknowledge that I owe my life’s chief occupation to God, so that every word and every thought of mine may speak of Him. But it is difficult to refute the errors of each individual, for two reasons. First, because the sacrilegious assertions of each erring individual are not so well known to us, that we are able from what they say to find arguments to refute their errors. For the Doctors of old used this method in order to confute the errors of the heathens, whose opinions they were able to know, since either they had been heathens themselves, or had lived among heathens and were conversant with their teachings. Secondly, because some of them, like the Mohammedans and pagans, do not agree with us as to the authority of any Scripture whereby they may be convinced, in the same way as we are able to dispute with the Jews by means of the Old Testament, and with heretics by means of the New: whereas the former accept neither. Wherefore it is necessary to have recourse to natural reason, to which all are compelled to assent. And yet this is deficient in the things of God.

And while we are occupied in the inquiry about a particular truth, we shall show what errors are excluded thereby, and how demonstrable truth is in agreement with the faith of the Christian religion.


Book I, Chapter 03. In What Way It Is Possible to Make Known the Divine Truth

Since, however, not every truth is to be made known in the same way, and it is the part of an educated man to seek for conviction in each subject, only so far as the nature of the subject allows, as the Philosopher most rightly observes as quoted by Boethius, it is necessary to show first of all in what way it is possible to make known the aforesaid truth.

Now in those things which we hold about God there is truth in two ways. For certain things that are true about God wholly surpass the capability of human reason, for instance that God is three and one: while there are certain things to which even natural reason can attain, for instance that God is, that God is one, and others like these, which even the philosophers proved demonstratively of God, being guided by the light of natural reason.

That certain divine truths wholly surpass the capability of human reason, is most clearly evident. For since the principle of all the knowledge which the reason acquires about a thing, is the understanding of that thing’s essence, because according to the Philosopher’s teaching the principle of a demonstration is what a thing is, it follows that our knowledge about a thing will be in proportion to our understanding of its essence. Wherefore, if the human intellect comprehends the essence of a particular thing, for instance a stone or a triangle, no truth about that thing will surpass the capability of human reason. But this does not happen to us in relation to God, because the human intellect is incapable by its natural power of attaining to the comprehension of His essence: since our intellect’s knowledge, according to the mode of the present life, originates from the senses: so that things which are not objects of sense cannot be comprehended by the human intellect, except in so far as knowledge of them is gathered from sensibles. Now sensibles cannot lead our intellect to see in them what God is, because they are effects unequal to the power of their cause. And yet our intellect is led by sensibles to the divine knowledge so as to know about God that He is, and other such truths, which need to be ascribed to the first principle. Accordingly some divine truths are attainable by human reason, while others altogether surpass the power of human reason.

Again. The same is easy to see from the degrees of intellects. For if one of two men perceives a thing with his intellect with greater subtlety, the one whose intellect is of a higher degree understands many things which the other is altogether unable to grasp; as instanced in a yokel who is utterly incapable of grasping the subtleties of philosophy. Now the angelic intellect surpasses the human intellect more than the intellect of the cleverest philosopher surpasses that of the most uncultured. For an angel knows God through a more excellent effect than does man, for as much as the angel’s essence, through which he is led to know God by natural knowledge, is more excellent than sensible things, even than the soul itself, by which the human intellect mounts to the knowledge of God. And the divine intellect surpasses the angelic intellect much more than the angelic surpasses the human. For the divine intellect by its capacity equals the divine essence, wherefore God perfectly understands of Himself what He is, and He knows all things that can be understood about Him: whereas the angel knows not what God is by his natural knowledge, because the angel’s essence, by which he is led to the knowledge of God, is an effect unequal to the power of its cause. Consequently an angel is unable by his natural knowledge to grasp all that God understands about Himself: nor again is human reason capable of grasping all that an angel understands by his natural power. Accordingly just as a man would show himself to be a most insane fool if he declared the assertions of a philosopher to be false because he was unable to understand them, so, and much more, a man would be exceedingly foolish, were he to suspect of falsehood the things revealed by God through the ministry of His angels, because they cannot be the object of reason’s investigations.

Furthermore. The same is made abundantly clear by the deficiency which every day we experience in our knowledge of things. For we are ignorant of many of the properties of sensible things, and in many cases we are unable to discover the nature of those properties which we perceive by our senses. Much less therefore is human reason capable of investigating all the truths about that most sublime essence.
With this the saying of the Philosopher is in accord (2 Metaph.) where he says that our intellect in relation to those primary things which are most evident in nature is like the eye of a bat in relation to the sun.

To this truth Holy Writ also bears witness. For it is written (Job 11:7): Peradventure thou wilt comprehend the steps of God and wilt find out the Almighty perfectly? and (36:26): Behold God is great, exceeding our knowledge, and (1 Cor. 13:9): We know in part.
Therefore all that is said about God, though it cannot be investigated by reason, must not be forthwith rejected as false, as the Manicheans and many unbelievers have thought.


Book I, Chapter 04. That the Truth about Divine Things Attainable by Reason is Fittingly Proposed to Man as an Object of Belief

While then the truth of the intelligible things of God is twofold, one to which the inquiry of reason can attain, the other which surpasses the whole range of human reason, both are fittingly proposed by God to man as an object of belief. We must first show this with regard to that truth which is attainable by the inquiry of reason, lest it appears to some, that since it can be attained by reason, it was useless to make it an object of faith by supernatural inspiration. Now three disadvantages would result if this truth were left solely to the inquiry of reason. One is that few men would have knowledge of God: because very many are hindered from gathering the fruit of diligent inquiry, which is the discovery of truth, for three reasons. Some indeed on account of an indisposition of temperament, by reason of which many are naturally indisposed to knowledge: so that no efforts of theirs would enable them to reach to the attainment of the highest degree of human knowledge, which consists in knowing God. Some are hindered by the needs of household affairs. For there must needs be among men some that devote themselves to the conduct of temporal affairs, who would be unable to devote so much time to the leisure of contemplative research as to reach the summit of human inquiry, namely the knowledge of God. And some are hindered by laziness. For in order to acquire the knowledge of God in those things which reason is able to investigate, it is necessary to have a previous knowledge of many things: since almost the entire consideration of philosophy is directed to the knowledge of God: for which reason metaphysics, which is about divine things, is the last of the parts of philosophy to be studied. Wherefore it is not possible to arrive at the inquiry about the aforesaid truth except after a most laborious study: and few are willing to take upon themselves this labour for the love of a knowledge, the natural desire for which has nevertheless been instilled into the mind of man by God.

The second disadvantage is that those who would arrive at the discovery of the aforesaid truth would scarcely succeed in doing so after a long time. First, because this truth is so profound, that it is only after long practice that the human intellect is enabled to grasp it by means of reason. Secondly, because many things are required beforehand, as stated above. Thirdly, because at the time of youth, the mind, when tossed about by the various movements of the passions, is not fit for the knowledge of so sublime a truth, whereas calm gives prudence and knowledge, as stated in 7 Phys. Hence mankind would remain in the deepest darkness of ignorance, if the path of reason were the only available way to the knowledge of God: because the knowledge of God which especially makes men perfect and good, would be acquired only by the few, and by these only after a long time.

The third disadvantage is that much falsehood is mingled with the investigations of human reason, on account of the weakness of our intellect in forming its judgments, and by reason of the admixture of phantasms. Consequently many would remain in doubt about those things even which are most truly demonstrated, through ignoring the force of the demonstration: especially when they perceive that different things are taught by the various men who are called wise. Moreover among the many demonstrated truths, there is sometimes a mixture of falsehood that is not demonstrated, but assumed for some probable or sophistical reason which at times is mistaken for a demonstration. Therefore it was necessary that definite certainty and pure truth about divine things should be offered to man by the way of faith.

Accordingly the divine clemency has made this salutary commandment, that even some things which reason is able to investigate must be held by faith: so that all may share in the knowledge of God easily, and without doubt or error.

Hence it is written (Eph. 4:17, 18): That henceforward you walk not as also the Gentiles walk in the vanity of their mind, having their understanding darkened: and (Isa. 54:13): All thy children shall be taught of the Lord.


Source: Saint Thomas Aquinas, Fathers of the English Dominican Province, Summa Contra Gentiles, vol. 1 (London: Burns Oates & Washbourne, 1924).
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