At the outset it is necessary to place a word of caution as to what is meant, in a question of this kind, by _certainty_. There are no limits to scepticism, as the history of speculative philosophy has abundantly shown. It is possible to question one's own existence, and still more possible to question the irresistible evidence of one's senses or the irresistible conclusions of one's reason. _A fortiori_ it is possible to throw doubt upon any historical fact. We can, if we like, classify the assassinations of Julius Caesar and of Cicero, and the genuineness of the AEneid and of the Epistles to the Corinthians, among things that are not certain. They cannot be demonstrated like a proposition in Euclid or an experiment in chemistry or physics. But a sceptical criticism of this kind makes history impossible; for it demands as a condition of certainty a kind of evidence, and an amount of evidence, which from the nature of the case is unattainable. Juries are directed by the courts to treat evidence as adequate, which they would be willing to recognize as such in matters of very serious moment to themselves. There is a certain amount of evidence which to a person of trained and well-balanced mind makes a thing "practically certain:" _i.e._, with this amount of evidence before him he would confidently act on the assumption that the thing was true.
In the question before us there are four or five things which may with great reason be treated as practically certain.
1. The solution of the question as to the origin of the Christian ministry, _has no practical bearing upon the lives of Christians_. For us the problem is one of historical interest without moral import. As students of Church History we are bound to investigate the _origines_ of the ministry which has been one of the chief factors in that history: but our loyalty as members of the Church will not be affected by the result of our investigations. Our duty towards the constitution consisting of bishops, priests, and deacons, which existed unchallenged from the close of the second century to the close of the Middle Ages, and which has existed down to the present day in all the three great branches of the Catholic Church, Roman, Oriental, and Anglican, is no way affected by the question whether the constitution of the Church during the century which separates the writings of St. John from the writings of his disciple's disciple, Irenaeus, was as a rule episcopal, collegiate, or presbyterian. For a churchman who accepts the episcopal form of government as essential to the well-being of a Church, the enormous prescription which that form has acquired during at least seventeen centuries, is such ample justification, that he can afford to be serene as to the outcome of enquiries respecting the constitution of the various infant Churches from A.D. 85 to A.D. 185. It makes no practical difference either to add, or not to add, to an authority which is already ample. To prove that the episcopal form of government was founded by the Apostles may have been a matter of great practical importance in the middle of the second century. But, before that century had closed, the practical question, _if there ever was one_, had settled itself. God's providence ordained that the universal form of Church government should be the episcopal form and should continue to be such; and for us it adds little to its authority to know that the way in which it became universal was through the instrumentality and influence of Apostles. On the other hand, to prove that episcopacy was established independently of Apostolic influence would detract very little from its accumulated authority.
2. A second point, which may be regarded as certain with regard to this question, is, that _for the period which joins the age of Irenaeus to the age of St. John, we have not sufficient evidence to arrive at anything like proof_. The evidence has received important additions during the present century, and still more important additions are by no means impossible; but at present our materials are still inadequate. And the evidence is insufficient in two ways. First, although surprisingly large as compared with what might have been reasonably expected, yet in itself, the literature of this period is fragmentary and scanty. Secondly, the dates of some of the most important witnesses cannot as yet be accurately determined. In many cases to be able to fix the date of a document within twenty or thirty years is quite sufficient: but this is a case in which the difference of twenty years is a really serious difference; and there is fully that amount of uncertainty as to the date of some of the writings which are our principal sources of information; _e.g._, the _Doctrine of the Twelve Apostles_, the Epistles of Ignatius, the _Shepherd of Hermas_ and the _Clementines_. Here also our position may improve. Further research may enable us to date some of these documents accurately. But, for the present, uncertainty about precise dates and general scantiness of evidence compel us to admit that with regard to many of the points connected with this question nothing that can fairly be called proof is possible respecting the interval which separates the last quarter of the first century from the last quarter of the second.