In like manner the mind also, or animus, which the Greeks designate ΝΟΥΣ, is taken by us in no other sense than as indicating that faculty or apparatus which is inherent and implanted in the soul, and naturally proper to it, whereby it acts, whereby it acquires knowledge, and by the possession of which it is capable of a spontaneity of motion within itself, and of thus appearing to be impelled by the mind, as if it were another substance, as is maintained by those who determine the soul to be the moving principle of the universe—the god of Socrates, Valentinus’ “only-begotten” of his father Bythus, and his mother Sige.
…We, however, affirm that the mind coalesces with the soul,—not indeed as being distinct from it in substance, but as being its natural function and agent.
Tertullian
A Treatise on the Soul
Chapter XII