Valentinus left the church before inventing his heresy

Valentinus had expected to become a bishop, because he was an able man both in genius and eloquence. Being indignant, however, that another obtained the dignity by reason of a claim which confessorship had given him, he broke with the church of the true faith. Just like those (restless) spirits which, when roused by ambition, are usually inflamed with the desire of revenge, he applied himself with all his might to exterminate the truth; and finding the clue of a certain old opinion, he marked out a path for himself with the subtlety of a serpent. Ptolemæus afterwards entered on the same path, by distinguishing the names and the numbers of the Ænons into personal substances, which, however, he kept apart from God. Valentinus had included these in the very essence of the Deity, as senses and affections of motion. Sundry bypaths were then struck off therefrom, by Heraclean and Secundus and the magician Marcus. Theotimus worked hard about “the images of the law.” Valentinus, however, was as yet nowhere, and still the Valentinians derive their name from Valentinus. Axionicus at Antioch is the only man who at the present time does honour to the memory of Valentinus, by keeping his rules to the full. But this heresy is permitted to fashion itself into as many various shapes as a courtezan, who usually changes and adjusts her dress every day. And why not?  When they review that spiritual seed of theirs in every man after this fashion, whenever they have hit upon any novelty, they forthwith call their presumption a revelation, their own perverse ingenuity a spiritual gift; but (they deny all) unity, admitting only diversity.

Tertullian
Against the Valentinians
Chapter IV

Matter had no prior existence

Therefore, in as far as it has become evident that Matter had no prior existence (even from this circumstance, that it is impossible for it to have had such an existence as is assigned to it), in so far is it proved that all things were made by God out of nothing. It must be admitted, however, that Hermogenes, by describing for Matter a condition like his own—irregular, confused, turbulent, of a doubtful and precipate and fervid impulse—has displayed a specimen of his own art, and painted his own portrait.

Tertullian
Against Hermogenes
Chapter XLV

Hermogenes has a low view of matter

Does that which is good never desire, never wish, never feel able to advance, so as to change its good for a better? And in like manner, if Matter had been by nature evil, why might it not have been changed by God as the more powerful Being, as able to convert the nature of stones into children of Abraham? Surely by such means you not only compare the Lord with Matter, but you even put Him below it, since you affirm that the nature of Matter could not possibly be brought under control by Him, and trained to something better.

Tertullian
Against Hermogenes
Chapter XXXVII

The Holy Spirit created all things and the Scriptures are His

And to such a degree has the Holy Ghost made this the rule of His Scripture, that whenever anything is made out of anything, He mentions both the thing that is made and the thing of which it is made. “Let the earth,” says He, “bring forth grass, the herb yielding seed, and the fruit-tree yielding fruit after its kind, whose seed is in itself, after its kind.

…if the Holy Ghost took upon Himself so great a concern for our instruction, that we might know from what everything was produced, would He not in like manner have kept us well informed about both the heaven and the earth, by indicating to us what it was that He made them of, if their original consisted of any material substance, so that the more He seemed to have made them of nothing, the less in fact was there as yet made, from which He could appear to have made them?

Tertullian
Against Hermogenes
Chapter XXII

The Logos is begotten from within God, not outside of him

Indeed, as soon as He perceived It to be necessary for His creation of the world, He immediately creates It, and generates It in Himself. “The Lord,” says the Scripture, “possessed me, the beginning of His ways for the creation of His works. Before the worlds He founded me; before He made the earth, before the mountains were settled in their places; moreover, before the hills He generated me, and prior to the depths was I begotten.” Let Hermogenes then confess that the very Wisdom of God is declared to be born and created, for the especial reason that we should not suppose that there is any other being than God alone who is unbegotten and uncreated. For if that, which from its being inherent in the Lord was of Him and in Him, was yet not without a beginning,—I mean His wisdom, which was then born and created, when in the thought of God It began to assume motion for the arrangement of His creative works,—how much more impossible is it that anything should have been without a beginning which was extrinsic to the Lord!

Tertullian
Against Hermogenes
Chapter XVIII

God created all things out of nothing, not forming them from any existing material

If any material was necessary to God in the creation of the world, as Hermogenes supposed, God had a far nobler and more suitable one in His own wisdom—one which was not to be gauged by the writings of philosophers, but to be learnt from the words or prophets. This alone, indeed, knew the mind of the Lord. For “who knoweth the things of God, and the things in God, but the Spirit, which is in Him?” Now His wisdom is that Spirit. This was His counsellor, the very way of His wisdom and knowledge. Of this He made all things, making them through It, and making them with It.

Tertullian
Against Hermogenes
Chapter XVIII

We are made gods by grace and not by any property of our own

Well, then, you say, we ourselves at that rate possess nothing of God. But indeed we do, and shall continue to do—only it is from Him that we receive it, and not from ourselves. For we shall be even gods, if we, shall deserve to be among those of whom He declared, “I have said, Ye are gods,” and, “God standeth in the congregation of the gods.” But this comes of His own grace, not from any property in us, because it is He alone who can make gods.

Tertullian
Against Hermogenes
Chapter V

There is only one God and Father of all

For “although there be that are called gods” in name, “whether in heaven or in earth, yet to us there is but one God the Father, of whom are all things;” whence the greater reason why, in our view, that which is the property of God ought to be regarded as pertaining to God alone, and why (as I have already said) that should cease to be such a property, when it is shared by another being. Now, since He is God, it must necessarily be a unique mark of this quality, that it be confined to One. Else, what will be unique and singular, if that is not which has nothing equal to it? What will be principal, if that is not which is above all things, before all things, and from which all things proceed? By possessing these He is God alone, and by His sole possession of them He is One.  If another also shared in the possession, there would then be as many gods as there were possessors of these attributes of God.

Tertullian
Against Hermogenes
Chapter IV