18. What do the Persons of the Trinity have in common or as their own?

D. What do each of the Persons of the Trinity have as their own? M. The fact that the Father is never called the Son, nor in related terms the Holy Spirit, although separately he may be called both Spirit and holy. Nor can the Son properly be called the Father or, conformably, the Holy Spirit. Nor again is the name of 'Father' or 'Son' ascribed to the Holy Spirit.

[2] D. Which things are common to these Persons? M. All things which are acknowledged to pertain to the indication either of essence or operation or comparison to creatures, whence even it is agreed that the Trinity is of one substance [by the terms 'Father' and 'Son' and 'Holy Spirit'].

[3] D. What is indicated in these Persons? M. Not what they are, but that they are. For what they are (as above we said about God) speech is not able to unfold.