3 But lest any from lack of learning, should suppose from the different titles of the Holy Ghost that these are various spirits, and not one and the self-same, which alone there is, therefore the Catholic Church guarding you beforehand has delivered to you in the profession of the faith, that you “believe in one Holy Ghost the Comforter, who spoke by the Prophets;” that you might know, that though His names be many, the Holy Spirit is but one—of which names, we will now rehearse to you a few out of many.
Source: Catechetical Lectures (New Advent)