He is perhaps most famous for coining the term Trinity (Latin trinitas) and giving the first exposition of the formula. Other formulations that first appear in his work are "three Persons, one Substance" as the Latin "tres Personae, una Substantia" (itself from the Koine Greek "treis Hypostases, Homoousios"), and also the terms vetus testamentum ("old testament") and novum testamentum ("new testament").
Scanty reliable evidence exists to inform us about Tertullian's life, mostly coming from passing references in his own writings.
He was raised in Carthage as a pagan. Traditionally he has been thought to be the son of a Roman centurion, a trained lawyer, and an ordained priest; however, these assertions rely on the accounts of Eusebius of Caesarea, Church History, II, ii. 4, and Jerome's De viris illustribus (On famous men) chapter 53. Jerome claimed that Tertullian's father held the position of 'centurio proconsularis' ("aide-de-camp") in the Roman army in Africa; however, it is unclear whether any such position in the Roman military ever existed.. Additionally, Tertullian has been thought to be a lawyer based on his use of legal analogies and an identification of him with the jurist Tertullianus, who is quoted in the Pandects. Although Tertullian utilized a knowledge of Roman law in his writings, his legal knowledge does not demonstrably exceed that of what could be expected from a sufficient Roman education.The writings of Tertullianus, a lawyer of the same cognomen, exist only in fragments and do not denote a Christian authorship. Tertullianus was only identified with the Christian Tertullian by church historians much later. Finally, any notion of Tertullian being a priest is also questionable. In his extant writings, he never describes himself as ordained in the church and seems to place himself among the laity.
Roman Africa was famous as the home of orators, and this influence can be seen in his style, with its archaisms or provincialisms, its glowing imagery and its passionate temper. He was a scholar, having received an excellent education. He wrote at least three books in Greek, to which he himself refers; but none of these are extant. His principal study was jurisprudence, and his methods of reasoning reveal striking marks of his juridical training. He shone among the advocates of Rome, as Eusebius reports.
His conversion to Christianity perhaps took place about 197–198 (cf. Adolf Harnack, Bonwetsch, and others), but its immediate antecedents are unknown except as they are conjectured from his writings. The event must have been sudden and decisive, transforming at once his own personality; he himself said that he could not imagine a truly Christian life without such a conscious breach, a radical act of conversion: "Christians are made, not born" (Apol, xviii).
Two books addressed to his wife confirm that he was married to a Christian wife. In middle life (about 207) he was attracted to the "New Prophecy" of Montanism, and seems to have split from the mainstream church. In the time of Augustine, a group of "Tertullianists" still had a basilica in Carthage, but in that same period passed into the orthodox Church. It is unknown whether they were merely another name for Montanists, or whether this means that Tertullian later split with the Montanists and founded his own group.
Jerome says that Tertullian lived to a great age. In spite of his schism, Tertullian continued to write against heresy, especially Gnosticism; and by the doctrinal works thus produced he became the teacher of Cyprian, the predecessor of Augustine, and the chief founder of Latin theology.
The writings may be divided with reference to the two periods of Tertullian's Christian activity, the Catholic and the Montanist (cf. Harnack, ii.262 sqq.), or according to their subject-matter. The object of the former mode of division is to show, if possible, the change of views Tertullian's mind underwent. Following the latter mode, which is of a more practical interest, the writings fall into two groups. Apologetic and polemic writings, like Apologeticus, De testimonio animae, Adv. Judaeos, Adv. Marcionem, Adv. Praxeam, Adv. Hermogenem, De praescriptione hereticorum, Scorpiace counteract Gnosticism etc. The other writings are practical and disciplinary, e.g., De monogamia, Ad uxorem, De virginibus velandis, De cultu feminarum, De patientia, De pudicitia, De oratione, Ad martyras etc.
Among the apologetic writings the Apologeticus, addressed to the Roman magistrates, is the most pungent defense of Christianity and the Christians ever written against the reproaches of the pagans, and one of the most magnificent legacies of the ancient Church, full of enthusiasm, courage, and vigor. It first clearly proclaims the principle of freedom of religion as an inalienable right of man, and demands a fair trial for the Christians before they are condemned to death.
Tertullian was the first to break the force of such charges as that the Christians sacrificed infants at the celebration of the Lord's Supper and committed incest; he pointed to the commission of such crimes in the pagan world, and then proved by the testimony of Pliny that Christians pledged themselves not to commit murder, adultery, or other crimes; he adduced also the inhumanity of pagan customs, such as feeding the flesh of gladiators to beasts. The gods have no existence, and thus there is no pagan religion against which Christians may offend. Christians do not engage in the foolish worship of the emperors; they do better, they pray for them. Christians can afford to be put to torture and to death, and the more they are cast down the more they grow; "In the blood of the martyrs lies the seed of the Church" (Apologeticum, 1). In the De Praescriptione he develops as its fundamental idea that, in a dispute between the Church and a separating party, the whole burden of proof lies with the latter, as the Church, in possession of the unbroken tradition, is by its very existence a guarantee of its truth.
The five books against Marcion, written 207 or 208, are the most comprehensive and elaborate of his polemical works, invaluable for the understanding of Gnosticism. Of the moral and ascetic treatises, the De patientia and De spectaculis are among the most interesting, and the De pudicitia and De virginibus velandis among the most characteristic.
Let them produce the original records of their churches; let them unfold the roll of their bishops, running down in due succession from the beginning in such a manner that [that first bishop of theirs] bishop shall be able to show for his ordainer and predecessor some one of the apostles or of apostolic men, — a man, moreover, who continued steadfast with the apostles. For this is the manner in which the apostolic churches transmit their registers: as the church of Smyrna, which records that Polycarp was placed therein by John; as also the church of Rome, which makes Clement to have been ordained in like manner by Peter. In exactly the same way the other churches likewise exhibit (their several worthies), whom, as having been appointed to their episcopal places by apostles, they regard as transmitters of the apostolic seed.
On the principle that we should not look at or listen to what we have no right to practise, and that polluted things, seen and touched, pollute (De spectaculis, viii, xvii), he declared a Christian should abstain from the theater and the amphitheater. There pagan religious rites were applied and the names of pagan divinities invoked; there the precepts of modesty, purity, and humanity were ignored or set aside, and there no place was offered to the onlookers for the cultivation of the Christian graces. Women should put aside their gold and precious stones as ornaments (De cultu, v-vi), and virgins should conform to the law of St. Paul for women and keep themselves strictly veiled (De virginibus velandis). He praised the unmarried state as the highest (De monogamia, xvii; Ad uxorem, i.3), called upon Christians not to allow themselves to be excelled in the virtue of celibacy by Vestal Virgins and Egyptian priests, and he pronounced second marriage a species of adultery (De exhortations castitatis, ix).
Those who believe Tertullian went to an unhealthy extreme in his counsels of asceticism, might easily forgive him because of his moral vigor and the great service he provided as an ingenious and intrepid defender of the Christian religion. With Tertullian, as with Martin Luther and John Wesley, Christianity was first and chiefly an experience of the heart.
Tertullian is occasionally considered as an example of the misogyny of the early Church Fathers, on the basis of the contents of his 'De Cultu Feminarum,' section I.I, part 2 (trans. C.W. Marx): "Do you not know that you are Eve? The judgment of God upon this sex lives on in this age; therefore, necessarily the guilt should live on also. You are the gateway of the devil; you are the one who unseals the curse of that tree, and you are the first one to turn your back on the divine law; you are the one who persuaded him whom the devil was not capable of corrupting; you easily destroyed the image of God, Adam. Because of what you deserve, that is, death, even the Son of God had to die.”
Tertullian wrote in his in his book On Patience 5:15 "Having been made pregnant by the seed of the devil ... she brought forth a son."
"Now these signs of degradation quite suit His first coming, just as the tokens of His majesty do His second advent, when He shall no longer remain 'a stone of stumbling and rock of offence,' but after His rejection become 'the chief corner-stone,' accepted and elevated to the top place of the temple, even His church, being that very stone in Daniel, cut out of the mountain, which was to smite and crush the image of the secular kingdom. Of this advent the same prophet says: 'Behold, one like the Son of man came with the clouds of heaven, and came to the Ancient of days; and they brought Him before Him, and there was given Him dominion and glory, and a kingdom, that all people, nations, and languages should serve Him. His dominion is an everlasting dominion, which shall not pass away; and His kingdom that which shall not be destroyed.
" 'For that day shall not come, unless indeed there first come a falling away,' he [Paul] means indeed of this present empire, 'and that man of sin be revealed,' that is to say, Antichrist, 'the son of perdition, who opposeth and exalteth himself above all that is called God or religion; so that he sitteth in the temple of God, affirming that he is God. Remember ye not, that when I was with you, I used to tell you these things? And now ye know what detaineth, that he might be revealed in his time. For the mystery of iniquity doth already work; only he who now hinders must hinder, until he be taken out ol. the way.' What obstacles is there but the Roman state, the falling away of which, by being scattered into the ten kingdoms, shall introduce Antichrist upon (its own ruins)? And then shall be revealed the wicked one, whom the Lord shall consume with the spirit of His mouth, and shall destroy with the brightness of His coming: even him whose coming is after the working of Satan, with all power, and signs, and lying wonders, and with all deceivableness of unrighteousness in them that perish.'
"So, again, Babylon, in our own John, is a figure of the city Rome, as being equally great and proud of her sway, and triumphant over the saints.
He depicts her as "drunk" with the blood of martyred "saints." Such was the obviously immediate application.
"There is also another and a greater necessity for our offering prayer in behalf of the emperors, nay, for the complete-stability of the empire, and for Roman interests in general. For we know that a mighty shock impending over the whole earth — in fact, the very end of all things threatening dreadful woes — is only retarded by the continued existence of the Roman empire. We have no desire, then, to be overtaken by these dire events; and in praying that their coming may be delayed, we are lending our aid to Rome's duration.
"Our inquiry relates to what is promised in heaven, not on earth. But we do confess that a kingdom is promised to us upon the earth, although before heaven, only in another state of existence; inasmuch as it will be after the resurrection for a thousand years in the divinely-built city of Jerusalem, 'let down from heaven,' which the apostle also calls 'our mother from above;' and, while declaring that our citizenship, is in heaven, he predicates of it that it is really a city in heaven. This both Ezekiel had knowledge of and the Apostle John beheld. . . .
"This city [new Jerusalem] has been provided by God for receiving the saints on their resurrection, and refreshing them with the abundance of all really spiritual blessings, as a recompense for those which in the world we have either despised or lost; since it is both just and God-worthy that His servants should have their joy in the place where they have also suffered affliction for His name's sake.
"Of the heavenly kingdom this is the process. After its thousand years are over, within which period is completed the resurrection of the saints, who rise sooner or later according to their deserts, there will ensue the destruction of the world and the conflagration of all things at the judgment: we shall then be changed in a moment into the substance of angels, even by the investiture of an incorruptible nature, and so be removed to that kingdom in heaven.