That the Holy Ghost is a Subsistent Person

BUT inasmuch as some have maintained that the Holy Ghost is not a subsistent Person, but is either the divinity of the Father and the Son (cf. St Aug. de haeresibus, n. 52), or some accidental perfection of the mind given us by God, as wisdom, or charity, or other such created accidents, we must evince the contrary.

1. Accidental forms do not properly work, but the subject that has them works according to the arbitrement of his own will: thus a wise man uses wisdom when he wills. But the Holy Ghost works according to the arbitrement of His own will (1 Cor. xii, 11).

2. The Holy Ghost is not to be accounted an accidental perfection of the human mind, seeing that He is the cause of such perfections: for the charity of God is spread abroad in our hearts by the Holy Ghost who is given to us (Rom. v, 5): To one is given by the Spirit the utterance of wisdom, to another the utterance of knowledge according to the same Spirit (1 Cor. xii, 8).

3. The Holy Ghost proceeds from the Father and receives from the Son (John xv, 26: xvi, 14): which cannot be understood of the divine essence.

4. Scripture speaks of the Holy Ghost as of a subsistent Person: The Holy Ghost said to them: Set aside for me Barnabas and Saul for the work unto which I have taken them: . . . . and they, sent by the Holy Ghost, went (Acts xiii, 2, 4,): It hath seemed good to the Holy Ghost and us (Acts xv, 28).

5. The Father and the Son being subsistent Persons and of divine nature, the Holy Ghost would not be numbered with them (Matt. xxviii, 19: 2 Cor. xiii, 13: 1 John v, 7) were He not a Person subsistent in the divine nature.

4.17 : That the Holy Ghost is true God
4.20 : Of the Effects which the Scriptures attribute to the Holy Ghost in respect of the whole Creation