The Unity and Trinity of God
The Dogma of the Trinity
The Doctrinal Decisions of the Church
#34 In God there are Three Persons, the Father, the Son and the Holy Ghost. Each of the Three Persons possesses the one (numerical) Divine Essence.
The Internal Divine Processions in General
#35 In God there are two Internal Divine Processions.
#36 The Divine Persons, not the Divine Nature, are the subject of the Internal Divine processions (in the active and in the passive sense).
The Procession of the Son from the Father by Way of Generation
#37 The Second Divine Person proceeds from the First Divine Person by Generation, and therefore is related to Him as Son to a Father.
The Procession of the Holy Ghost from the Father and the Son by way of Spiration
#38 The Holy Ghost proceeds from the Father and from the Son as from a Single Principle through a Single Spiration.
#39 The Holy Ghost does not proceed through generation but through spiration.
The Divine Relations
#40 The Relations in God are really identical with the Divine Nature.
The Divine Persons
#41 In God all is one except for the opposition of relations.
The Trinitarian Perichoresis (Circumincession)
#42 The Three Divine Persons are in One Another.
The Unity of the Divine Operation ad extra
#43 All the ad extra Activities of God are common to the Three Persons.