Certain ecclesiastical historians (Jean Danielou and Jaroslav Pelikan) have argued that Tertullian possibly does not distinguish the three Persons of the Trinity, as one might expect, if he was really a Trinitarian qua Trinitarian. Reading Adv Praxean 12, I think they might be right. It says:
"If you are still offended by the plurality of the Trinity, on the ground that it is not combined in simple unity, I ask you how it, is that one only single
speaks in the plural, Let us make man after our image and likeness,1 when he ought to have said, Let me make man after my image and likeness, as being one only single . Also in what follows, Behold, Adam is become as one of us, he is deceptive or joking in speaking in the plural while being one and alone and singular. Or was he speaking to the angels, as the Jews explain it, because they, like you, do not recognise the Son? Or, because he was himself father-son-spirit, did he for that reason make himself plural and speak to himself in the plural? Nay rather, because there already was attached to him the Son, a second Person, his Word, and a third Person, the Spirit in the Word, for that reason he spoke in the plural, Let us make, and Our, and Of us."