We proceed to the fifth article thus:

1. It seems that a man can know that he has grace. For grace is in the soul through its essence, and the most certain knowledge that the soul can have is of what is in itself through its own essence (as Augustine proves in 12 Gen. ad Litt.31). Grace can therefore be known by him who has grace, with the greatest possible certainty.

2. Again, as knowledge is a gift from God, so also is grace. Now whosoever receives knowledge from God knows that he has knowledge, according to Wisdom 7:17: "the Lord hath given me true knowledge of the things that are." For a like reason, therefore, whosoever receives grace from God knows that he has grace.

3. Again, light is more easily known than darkness, since "whatsoever doth make manifest is light," [42] as the apostle says (Eph.5:13). But sin, which is spiritual darkness, can be known with certainty by him who has sin. Much more then can grace, which is spiritual light.

4. Again, the apostle says (I Cor.2:12): "Now we have received, not the spirit of the world, but the spirit which is of God; that we might know the things that are freely given to us of God." Now grace is the first gift of God. A man who has received grace through the Holy Spirit therefore knows that grace is given to him.

5. Again, the Lord himself said to Abraham: "now I know that thou fearest God" (Gen.22:12), that is, "I have made thee to know" -- and this is the fear of reverence, for which grace is essential. A man can therefore know that he has grace.

On the other hand: it is said in Eccl.9:1: "no man knoweth either love or hatred by all that is before them." [43] Now sanctifying grace makes a man worthy of the love of God. It follows that no man can know whether he has sanctifying grace.

I answer: there are three ways by which a thing may be known. One way is by revelation. A man may know by revelation that he has grace, since there are times when God reveals this to some as a special privilege, thus engendering within them the joy of security, even in this present life, in order that they may the more confidently and wholeheartedly carry out noble works, and withstand the evils of this present life. Thus was it said to Paul: "My grace is sufficient for thee" (II Cor.12:9).

In another way, a man may know something by himself, and that with certainty. But no man can know, in this way, that he has grace. For we can be certain of something only if we apprehend it through its own proper principle. In knowledge of this kind, we are certain of conclusions which can be demonstrated from indemonstrable and universal principles. But no one can be sure that he knows any conclusion if he does not know its principle. Now the principle of grace is God himself, who is also its object, and God is unknown by us on account of his excellence. As Job says: "Behold, God is great, and we know him not" (36:26). Neither his presence in us nor his absence can be known with certainty. As Job says again: "Lo, he goeth by me, and I see him not: he passeth on also, but I perceive him not" (9:11). It follows that a man cannot judge with certainty whether he has grace. As it is said in I Cor.4:3-4: "yea, I judge not mine own self. . . but he that judgeth me is the Lord."

In a third way, we may know something conjecturally by means of signs. Anyone may know, after this manner, that he has grace, in as much as he perceives that he delights in God and loves not the world, and in as much as he is not aware of any mortal sin within him. We may understand in this wise what is said in Rev.2:17: "To him that overcometh will I give to eat of the hidden manna . . . which no man knoweth, saving he that receiveth it." But such knowledge is imperfect, wherefore it is said by the apostle in I Cor.4:4: "I know nothing by myself; yet am I not hereby justified," and also in Ps.19:12-13: "Who can understand his errors? cleanse thou me from secret faults. Keep back thy servant also from presumptuous sins."

On the first point: what is in the soul through its essence is known by way of experimental awareness, in so far as a man knows inward principles through actions. We know the will through willing, for example, and we know life through the functions of life.

On the second point: certainty of what we know is essential to science. Certainty of what we hold in faith is likewise essential to faith. The reason for this is that certainty is a perfection of the intellect, in which such gifts exist. Whosoever has either knowledge or faith, therefore, is certain that he has it. But it is otherwise with grace and charity, and the like, because these are perfections of the appetitive power.

On the third point: the principle and the object of sin both consist in changeable good, which we know. But the object and end of grace is unknown to us on account of the immensity of its light, of which 1 Tim.6:16 says: "the light which no man can approach unto."

On the fourth point: the apostle is here speaking of the gifts of glory, the hope of which is given unto us. We know such things assuredly through faith, although we do not know assuredly that we have grace whereby we may merit them.

On the fifth point: what was said to Abraham may have referred to his experimental awareness, which his actions revealed. Abraham could have known, experimentally through his actions, that he feared God. Or it may refer to a revelation.

[42] Migne: "All that is made manifest is light."

[43] Migne: "No man knoweth whether he is worthy of hate or of love."