These two Latin phrases are open used in theology to indicate two different kinds of actions. Within contexts involving God's acts, ad intra signifies that the action and its effects are communicated and confined only within the Trinity, having no effect beyond them. In acting ad intra, the three Persons of the Trinity act independently and in clear distinction to one another.
Conversely, God's acts ad extra signifies that the action and its effect is taken among His creation, whence the Persons of the Trinity work together as one Doer and Maker (e.g., "Let us make man in our image," Gen 1:26).
The terms may also be used of human acts. When so applied, ad intra signifies acts that affect or result only in one's mind or self, as opposed to ad extra acts that impact the outside world.
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