I answer that, In prophetic revelation the prophet's mind is moved by the Holy Ghost, as an instrument that is deficient in regard to the principal agent. Now the prophet's mind is moved not only to apprehend something, but also to speak or to do something; sometimes indeed to all these three together, sometimes to two, sometimes to one only, and in each case there may be a defect in the prophet's knowledge. For when the prophet's mind is moved to think or apprehend a thing, sometimes he is led merely to apprehend that thing, and sometimes he is further led to know that it is divinely revealed to him.
Again, sometimes the prophet's mind is moved to speak something, so that he understands what the Holy Ghost means by the words he utters; like David who said ( 2 Kings 23:2): "The Spirit of the Lord hath spoken by me"; while, on the other hand, sometimes the person whose mind is moved to utter certain words knows not what the Holy Ghost means by them, as was the case with Caiphas ( Jn. 11:51 ).
Again, when the Holy Ghost moves a man's mind to do something, sometimes the latter understands the meaning of it, like Jeremias who hid his loin-cloth in the Euphrates ( Jer. 13:1-11 ); while sometimes he does not understand it---thus the soldiers, who divided Christ's garments, understood not the meaning of what they did.
Accordingly, when a man knows that he is being moved by the Holy Ghost to think something, or signify something by word or deed, this belongs properly to prophecy; whereas when he is moved, without his knowing it, this is not perfect prophecy, but a prophetic instinct. Nevertheless it must be observed that since the prophet's mind is a defective instrument, as stated above, even true prophets know not all that the Holy Ghost means by the things they see, or speak, or even do.
And this suffices for the Replies to the Objections, since the arguments given at the beginning refer to true prophets whose minds are perfectly enlightened from above.