Documentary evidence: A case study

By Doug Shaver
June 2014

Apologists routinely accuse us skeptics of applying a double standard to documentary evidence. Typically we hear something like: “If we applied your criteria across the board, we would know nothing about the past.” The criteria typically are about documentary evidence. Supposedly, we judge Christianity’s paper trail using standards that nobody applies to the source documents of secular history.

The cogency of this argument depends on the particular claims at issue and the kinds of documents used to support them. Rather than elaborate that point in detail, I offer something like a case study. It came up in an apologetics forum where I was hanging out a couple of years ago. My interlocutor presented the following argument:

If a skeptic rejects the traditional authorship of the Gospels while accepting the traditional authorship of other ancient historical works such as Caesar’s Gallic Wars, then the skeptic is unreasonably applying a different methodology to the Gospels, because the external evidence for traditional authorship of the Gospels is at least as strong as for Caesar’s authorship of Gallic Wars.

The original dialogue is no longer accessible, but I will note that I have edited the discussion quite a bit to accommodate change of context, improve readability, avoid copyright issues, and address a few of my interlocutor’s points that I passed over during the original exchange. I have also omitted a philosophical digression on the nature of evidence.

I began my response as follows, focusing on the Gospel According to Luke for the sake of rhetorical simplicity. My interlocutor’s remarks will be in italics.

My first argument is an appeal to scholarly consensus, which is basically an argument from authority. Although formally invalid, an argument from authority is inductively cogent when used properly. If authorities agree that some X is a fact, this does not actually establish that X is a fact, but it does justify an uninformed layman's belief that X is a fact. By uninformed, I mean that the layman has not personally investigated the evidence thoroughly enough to justify his forming an independent opinion. He is aware of the judgment of those who have investigated the evidence for themselves and are competent to assess its implications, and he has no factual basis on which to question their collective judgment.

So far as I am aware, there is zero disagreement among competent secular historians that Julius Caesar wrote most of the Gallic Wars. If I knew nothing else about the history of Rome, I would need no other reason to believe that Caesar wrote Gallic Wars. I do know a little more, actually, but it is all consistent with Caesar's authorship of that work So, I am aware of the scholarly consensus, and I am aware of no fact that is inconsistent with that consensus. That is all the justification I need for supposing, tentatively, that the consensus is correct.

My insertion of "tentatively" was very deliberate. I am convinced that no consensus should be immune to challenge. If I should learn that an apparently competent scholar claims to have found evidence that Caesar did not write the Gallic Wars, then I cannot justify saying that he must be wrong until I find out the exact nature of the evidence he has discovered and what kind of argument he uses to show that it disproves the consensus. But as I said, I don't know of any scholar who claims to have done that, and until I hear of one, I am entitled to accept the consensus.

Now, why do I think that a scholarly consensus is evidence for anything? Because, all else being equal, people who have examined the evidence for themselves and have been trained in how to assess that evidence are more likely to reach a true conclusion than a false conclusion as to what the evidence really proves, particularly if those people's judgment is unanimous or very nearly so. Given the natural quarrelsomeness of human nature and the diversity of human biases, a unanimous judgment in a field as inherently uncertain as history is a strong indicator that there really is only one plausible explanation for the evidence under consideration.

On the other hand, there is no such consensus among New Testament scholars about who wrote Luke's gospel. As best I can tell from extensive reading in the field, only a minority of relevant authorities accept the tradition that it was written by a physician whose name was Luke and who sometimes traveled with the apostle Paul. If I knew nothing else about New Testament studies or the history of Christianity, that fact alone would justify my doubting -- or at least withholding judgment about -- the traditional authorship of the third gospel. And, exactly the same argument would apply to the three other gospels. There is no scholarly consensus supporting the traditional authorship of any of them. If the experts cannot agree that the evidence proves X, then I am justified in supposing that the evidence for X is, at best, inconclusive.

That is, as already noted, if I am aware of no evidence except the opinions of the experts. As it happens, I have some familiarity with the evidence on which New Testament scholars base their opinions. And, it could be the case that I am familiar enough with that evidence to have a justified opinion as to whether the experts are justified in their opinion. And in the case of Luke, I believe they are.

The earliest nearly certain attestation of Luke's authorship is that of Irenaeus, ca. 180:

Matthew also issued a written Gospel among the Hebrews in their own dialect, while Peter and Paul were preaching at Rome, and laying the foundations of the Church. After their departure, Mark, the disciple and interpreter of Peter, did also hand down to us in writing what had been preached by Peter. Luke also, the companion of Paul, recorded in a book the Gospel preached by him. Afterwards, John, the disciple of the Lord, who also had leaned upon His breast, did himself publish a Gospel during his residence at Ephesus in Asia (Against Heresies, 3.1.1).

Probably around the same time, the author of the Muratorian Fragment asserts (bracketed material by translator):

The third book of the Gospel is that according to Luke. Luke, the well-known physician, after the ascension of Christ, when Paul had taken with him as one zealous for the law, composed it in his own name, according to [the general] belief.

There is nothing earlier, and neither writer gives any indication of their sources for this particular datum. Indeed, the MF author practically admits that he is simply reporting the consensus of his community. As for Irenaeus, we know that he was familiar with Papias's work, and it is possible that he was relying on Papias for his claim that Matthew and Mark wrote two of the gospels. However, he does not quote that portion of Papias -- we get that statement from Eusebius, well over a century later -- and no surviving quotation of Papias's writing mentions Luke at all.

Paul himself does attest, in three epistles, to having a friend named Luke, and in one he mentions that Luke was a physician, but he says nothing else about him. In particular, he says nothing about Luke's having written, or intending to write, an account of Jesus' ministry. This is not much of a problem, since Luke might have had no such intention at the time Paul was writing those epistles, and so we don't have a cogent argument from silence. The fact remains that there is no evidence from any contemporary of Luke that he wrote anything at all about Jesus or about anything else. A good explanation for lack of evidence of X does not itself constitute evidence of X.

Another fact in evidence, which is relevant to an assessment of Irenaeus's reliability as a historian, is the manifestly apologetic nature of his work. His primary purpose was the defense of certain religious doctrines, and he clearly believed that those doctrines were supported by the four gospels he was endorsing. It is hardly unreasonable to think that under those circumstances, he would have been powerfully predisposed to believe any story he heard about apostolic authorship of the gospels, no matter whom he heard the story from. Christian apologists will do that. We see it all the time today on the Internet, and we were seeing it all the time before there was any Internet. Therefore, any argument along the lines of "If Irenaeus believed it, he must have had a good reason to believe it" will not work. It is possible he had a good reason, but we don't know that he did, and possibility does not entail any probability.

So now, what about the Gallic Wars? The earliest direct attestation that I am aware of is Suetonius's. Here is the pertinent passage:

He [Caesar] has likewise left Commentaries of his own actions both in the war in Gaul, and in the civil war with Pompey; for the author of the Alexandrian, African, and Spanish wars is not known with any certainty. Some think they are the production of Oppius, and some of Hirtius; the latter of whom composed the last book, which is imperfect, of the Gallic war. Of Caesar's Commentaries, Cicero, in his Brutus, speaks thus: "He wrote his Commentaries in a manner deserving of great approbation: they are plain, precise, and elegant, without any affectation of rhetorical ornament. In having thus prepared materials for others who might be inclined to write his history, he may perhaps have encouraged some silly creatures to enter upon such a work, who will needs be dressing up his actions in all the extravagance a (37) bombast; but he has discouraged wise men from ever attempting the subject." Hirtius delivers his opinion of these Commentaries in the following terms: "So great is the approbation with which they are universally perused, that, instead of rousing, he seems to have precluded, the efforts of any future historian. Yet, with respect to this work, we have more reason to admire him than others; for they only know how well and correctly he has written, but we know, likewise, how easily and quickly he did it." Pollio Asinius thinks that they were not drawn up with much care, or with a due regard to truth; for he insinuates that Caesar was too hasty of belief in regard to what was performed by others under his orders; and that, he has not given a very faithful account of his own acts, either by design, or through defect of memory; expressing at the same time an opinion that Caesar intended a new and more correct edition (The Lives of the Twelve Caesars, 46).

Some observations follow.

Suetonius refers to histories of four wars, all attributed by some people to Caesar -- Gallic, Alexandrian, African, and Spanish -- and he notes that authorship of three of those histories is actually uncertain, but there seems to be no question about who wrote the history of the Gallic War, except the last book thereof. That, says Suetonius, was written by Hirtius, who some people think was also the author of the other three histories. In any case, Hirtius was a contemporary of Caesar and, at least by reputation, about as good a writer as Caesar, since it was possible to mistake the work of one for that of the other.

So we have Suetonius quoting three previous writers as crediting Caesar with writing the Gallic commentaries -- Hirtius, Cicero, and Pollio. All three were contemporaries of Caesar and personally acquainted with him. Nothing survives of Pollio's work. We have some of Hirtius's work if he wrote the any of the Alexandrian, African, or Spanish wars, but there is no mention in them of who wrote the Gallic Wars. We'll have a closer look at Cicero in a moment, but the point here is that Suetonius, unlike Irenaeus, does cite sources for what he says about who wrote the Gallic Wars. If all else were equal, that would suffice to justify our giving him more credence than we give Irenaeus. If we believe what Irenaeus said, we must believe it just because he said so, because we don't know why he said so. But we know why Suetonius said what he did, because he tells us why, and so we’re not just taking his word for it.

Let's look now at the pertinent passage from Cicero's Brutus dialogue (which, by the way, was written about two years before Caesar's assassination).

“But Caesar, who was guided by the principles of art, has corrected the imperfections of a vicious custom, by adopting the rules and improvements of a good one, as he found them occasionally displayed in the course of polite conversation. Accordingly, to the purest elegance of expression, (which is equally necessary to every well-bred Citizen, as to an Orator) he has added all the various ornaments of Elocution; so that he seems to exhibit the finest painting in the most advantageous point of view. As he has such extraordinary merit even in the common run of his language, I must confess that there is no person I know of, to whom he should yield the preference.

"Besides, his manner of speaking, both as to his voice and gesture, is splendid and noble, without the least appearance of artifice or affectation: and there is a dignity in his very presence, which bespeaks a great and elevated mind."

—"Indeed," said Brutus, "his Orations please me highly; for I have had the satisfaction to read several of them. He has likewise wrote some commentaries, or short memoirs, of his own transactions;"

—"and such," said I, "as merit the highest approbation: for they are plain, correct, and graceful, and divested of all the ornaments of language, so as to appear (if I may be allowed the expression) in a kind of undress.

"But while he pretended only to furnish the loose materials, for such as might be inclined to compose a regular history, he may, perhaps, have gratified the vanity of a few literary Frisseurs: but he has certainly prevented all sensible men from attempting any improvement on his plan. For in history, nothing is more pleasing than a correct and elegant brevity of expression. With your leave, however, it is high time to return to those Orators who have quitted the stage of life." (261-62)

Suetonius's quotation does not quite match this. The oldest surviving manuscripts of the Brutus are from late Medieval times, so it might be reasonable to suppose Suetonius's version is more accurate. Alternatively, on the (improbable) assumption that we have an exact copy of what Cicero wrote, we could suppose that Suetonius was slightly paraphrasing Cicero, making explicit what he assumed Cicero meant to imply. From the wording in Brutus as we have it, the assumption is hardly unreasonable. Maybe we ourselves should not make the assumption, but that doesn't mean Suetonius was unlikely to make it.

What Cicero does attest to, if nothing else, is that Caesar’s contemporaries believed that he did write many works and that some of them were known as commentaries, even if this passage does not make clear what they were commentaries about. In contrast, the single contemporaneous reference to Luke does not claim that he wrote anything at all.

So, Suetonius reports that three acquaintances of Julius Caesar gave him credit for writing the Gallic Wars, and that was apparently the main reason Suetonius himself had for claiming that Caesar was the author. Any argument against Caesar's authorship would have to propose one of two alternative explanations for this evidence, both pretty improbable. (1) None of the three actually did credit Caesar with writing the Gallic Wars, and Suetonius was mistaken to believe that they did. (2) Although the three did credit Caesar, they were mistaken, but Suetonius didn’t know that.

In other words, to doubt Suetonius, we have to doubt either his sources or his understanding of those sources -- and we're talking about at least three sources, all of them apparently independent of one another. That is not the case with Irenaeus, because he doesn't give us any sources.

Finally, we may ask whether Suetonius might have had some polemical reason, analogous to religious apologetics, for being overly credulous about his sources, whatever they were. I am not aware of any ideological point he was trying to make that would have been more or less believable depending on who he could claim was the author of the Gallic Wars.

This demonstrates, it seems to me, that the evidence for Luke's authorship of the third gospel -- and by extension for all traditional attributions of gospel authorship -- is not, in all relevant respects, as good as the evidence for Caesar's authorship of the Gallic Wars. From this it follows that we skeptics are not guilty of inconsistency if we believe one but not the other.

Your first fallacy is an appeal to authority, and anonymous authority at that. You speak vaguely of “competent secular historians” and “New Testament scholars” but fail to cite a single one. Who are all these anonymous scholars? What are their qualifications? How do we know they are in fact competent as you claim?

To begin with, a fallacy, strictly speaking, is a flaw in a deductive argument. But we're not talking about deductive arguments here. We're talking about what we can reasonably believe based on probabilistic judgments from incomplete evidence. In other words, we have nothing to use but inductive arguments, and an appeal to authority is an acceptable inductive argument when used correctly.

Here is my inductive argument from authority on the present issue:

Premise 1: If at least half of all competent scholars doubt some proposition within their field of expertise, then I as a layman am justified in doubting that proposition, if the division of scholarly opinion is the only evidence of which I am aware.

Premise 2: At least half of all competent NT scholars doubt Luke's authorship of the gospel attributed to him.

Premise 3 (Assumed for the sake of immediate discussion only): I am aware of no evidence relating to gospel authorship except the division of scholarly opinion.

Conclusion: I am justified in doubting Luke's authorship of the gospel attributed to him.

These premises do justify the conclusion, and so to challenge the conclusion you must challenge at least one premise. You implicitly question the second premise, but your rhetorical questions do not actually challenge its factuality. You neither assert that it is false nor suggest that I have good reason to doubt it. And, until you present a good reason to doubt it, I am within my epistemic rights to believe it, because I know how much scholarly literature I have read on this subject.

I am not claiming that this guarantees I am right or that anybody who disagrees with me is wrong. Inductive arguments can never do that. I am not attempting to prove that my adversaries are mistaken. I am attempting to prove only that I am justified in thinking they are mistaken.

You’re also arguing from consensus. A widely held belief is not evidence that the belief is true even if the people holding that belief are experts. Furthermore, a consensus among scholars is subject to change over time. You could not have made this appeal a few hundred years ago, when the scholarly consensus favored the traditional authorship of Luke.

I have not appealed to any consensus about the authorship of Luke's gospel. I have noted that there is no consensus. As for there having been a consensus a few hundred years ago, that is irrelevant. Competent scholars do not presuppose that whatever was believed a few hundred years ago is more likely to be true than what is believed nowadays.

The situations are not relevantly similar. The history of the Roman empire is relatively noncontroversial. Christianity is nothing but controversial. It’s been under academic attack for a few hundred years. Practically speaking, there is no consensus about anything.

Yes, but why is that the case? The controversies exist precisely because scholars of Christian history do not agree on whether, or to what degree, the extant evidence about Christianity's origins supports any of Christianity's teachings about its origins. Some Christians claim that this is solely because of anti-Christian hostility. That is possibly true, but if used in defense of any Christian teaching it needs to be proven, not simply assumed. To reject skeptical scholarship on that basis alone is pure question-begging, which is inadmissible even in an inductive argument.

You say there are two pieces of evidence, one from Irenaeus and one from the Muratorian Fragment. You also say there is nothing earlier. But we do have sources possibly earlier than Irenaeus.

1. Anti-Marcionite Prologue, c.160-180 CE

[Luke], when the gospels were already written down, that according to Matthew in Judea, but that according to Mark in Italy, instigated by the holy spirit, in parts of Achaea wrote down this gospel, he who was taught not only by the apostle, who was not with the Lord in the flesh, but also by the other apostles, who were with the Lord…

2. The oldest known manuscript of the Gospel of Luke ascribes the book to him. This is P75, c.175-225 CE.

These next sources are probably later than Irenaeus and the Muratorian Canon, but it’s important to remember they are still at least earlier than Suetonius is to the Gallic Wars.

3. Clement of Alexandria, Stromata, 1.21, c. 200 CE.

And to prove that this is true, it is written in the Gospel by Luke as follows: And in the fifteenth year, in the reign of Tiberius Cæsar, the word of the Lord came to John, the son of Zacharias. And again in the same book: And Jesus was coming to His baptism, being about thirty years old, and so on.

4. Tertullian, Against Marcion, 4.2, early 3rd century.

[The] evangelical Testament has apostles for its authors, to whom was assigned by the Lord Himself this office of publishing the gospel. Since, however, there are apostolic men also, they are yet not alone, but appear with apostles and after apostles; because the preaching of disciples might be open to the suspicion of an affectation of glory, if there did not accompany it the authority of the masters, which means that of Christ, for it was that which made the apostles their masters. Of the apostles, therefore, John and Matthew first instil faith into us; while of apostolic men, Luke and Mark renew it afterwards. These all start with the same principles of the faith, so far as relates to the one only God the Creator and His Christ, how that He was born of the Virgin, and came to fulfil the law and the prophets.

5. Origen, as preserved by Eusebius, Church History, 6.25.3

And the third by Luke, the Gospel commended by Paul, and composed for Gentile converts.

That is seven sources – my five in addition to your two – attesting to Luke’s authorship, all of them earlier than Suetonius is to the Gallic Wars.

The key phrase in your statement is “possibly earlier.” Mere possibility does not entail any kind of probability. Furthermore, the author of the prologue is unknown and we have no idea where he was getting his information. It could have been Irenaeus, or he could have been using whatever source Irenaeus used, but in either case his testimony is not independent of Irenaeus's. Either way, the prologue adds nothing to what we get from Irenaeus. And, any sources that are probably later than Irenaeus and the Muratorian Canon, unless provably independent, cannot refute anything I have said.

P75 is the Bodmer papyrus. Who says it could have been written as early as 175? Weren’t you saying something about anonymous authorities? According to the Vatican Library, P75 was written “around the beginning of the third century,” and Nestle-Aland assigns it a probable date of early third century.

The total number of your sources is irrelevant if they're not independent. Once Irenaeus made his pronouncement, all the others could have just been taking his word for it that Luke wrote the third gospel. To prove they weren't, you need to quote them citing an identifiable source other than Irenaeus.

Your claim that Irenaeus gives no indication of his source is debatable as well. Eusebius, in his Church History, quotes a letter from Irenaeus to Florinus, in which Irenaeus says:

I remember the events of that time more clearly than those of recent years. For what boys learn, growing with their mind, becomes joined with it; so that I am able to describe the very place in which the blessed Polycarp sat as he discoursed, and his goings out and his comings in, and the manner of his life, and his physical appearance, and his discourses to the people, and the accounts which he gave of his intercourse with John and with the others who had seen the Lord. And as he remembered their words, and what he heard from them concerning the Lord, and concerning his miracles and his teaching, having received them from eyewitnesses of the “Word of life,” Polycarp related all things in harmony with the Scriptures.

This tells us that Irenaeus’ source of data was Polycarp, an associate of John and other eyewitnesses to Jesus. Can we say we have that clear of a line to Caesar for Seutonius’ source(s)? We don’t know who Suetonius’ sources were. In fact, in reference to authorship Suetonius says “some think” indicating his source was merely the proverbial word on the street.

To start with, we have no word from Polycarp himself about him knowing any of Jesus’ disciples. That letter of Irenaeus apparently no longer exists, since otherwise we wouldn’t need Eusebius to tell us what was in it, and the quoted portion does not attest to Polycarp’s saying anything about who wrote any gospel. It does not say that Polycarp even confirmed so much as the existence of any document we would recognize as one of the canonical gospels.

Furthermore, I don't place a lot of confidence in what old men remember about their youth -- and I speak as one who happens to be an old man. With that noted, I will stipulate that Irenaeus did meet Polycarp. In that case, I find it highly improbable that, if Polycarp had told him something like, "You know that gospel with Luke's name on it? Luke actually wrote it, you know. John told me so himself," Irenaeus would not have said so either somewhere in his extant works or in that letter Eusebius was quoting. And if the letter did have some statement to that effect, there is no way Eusebius would have failed to say so.

We’re talking about seven sources. Do you think they all could have been mistaken?

Where is the improbability in that? If all seven were simply trusting whoever first said so, and if we don't even know who that first person was, then why should we be surprised if it happened not to be so? That sort of thing constantly happens. You would have us treat the patristic writers as if they were different from ordinary people. We're not talking here about the leadership of the Near Eastern Skeptics Society.

You claim that Irenaeus was biased. This is the genetic fallacy, and it is undermined by the fact that Luke and Mark were not apostles anyway. Tertullian makes the following point:

Luke, however, was not an apostle, but only an apostolic man; not a master, but a disciple, and so inferior to a master— at least as far subsequent to him as the apostle whom he followed (and that, no doubt, was Paul) was subsequent to the others. (Against Marcion, 4.2)

We would have expected Irenaeus (or another early Christian source) to attribute the authorship of Luke’s gospel (and Mark’s for that matter) to one of the disciples of Jesus – i.e. an apostle. But no, we have what was “only an apostolic man” who was “inferior to a master” with Luke. This adds to Irenaeus’ credibility since he reported what he knew even if it would potentially diminish the weight of the account.

You might have had a point if I had claimed that Irenaeus was just making everything up, but that isn’t what I said. I’m assuming that somebody told him Luke wrote a gospel and that he believed it for no better reason than (1) he had no information to the contrary and (2) it suited his apologetic purposes. And I assume that because, if he had had a better reason, he most likely would have said so. If you think he got it from Polycarp, you need to explain why he didn’t think that was worth mentioning.

Suetonius does not cite his sources. Suetonius believes the quote he provides is from Hirtius. But the quote itself that Suetonius gives is from the prologue of the final book of the Gallic Wars and is strictly speaking just as anonymous as each Gospel. The prologue could have been written by anyone at any time. So in fact what we have is Suetonius’ belief 170 years later that Cicero was referring to Caesar’s Gallic Wars in Brutus and that it was Hirtius who wrote the prologue to the final book. Since nothing of Asinius Pollio has survived he carries no more weight than say Papias.

At least in the case of Irenaeus we know that he had a direct link to his source Polycarp.

You’re confusing citation with credibility. Suetonius does say, in effect, “According to so-and-so, Caesar wrote the Gallic Wars.” Irenaeus says nothing of the sort concerning the authorship of Luke’s gospel. All he says is, “Luke wrote it.” We do not know that he got it from Polycarp. We do not know where he got it.

You wrote: “The single contemporary reference to Luke does not claim that he wrote anything.” This is of course an argument from silence.

I am making no argument from Paul’s silence. I am simply contrasting his actual silence regarding Luke’s literary activity with the alleged testimony, from people who knew Julius Caesar, that Caesar did a lot of writing, specifically including the writing of the Gallic Wars. That is a big difference in the evidence we have. Your claim is that one set of evidence is as good as the other. I am showing you why it is not.

You are disputing the unanimous attribution of the early church.

Unless you’re going to count abstentions as yes votes, the testimony of the early church is not unanimous. Nobody before Irenaeus says one word about who wrote the third gospel, and if we count only extant writings, none of them says a word about who wrote any gospel. And, nobody writing after Irenaeus can be presumed independent of him. We’re left with one source who says not a word about where he got his information. Suetonius identifies three sources for his claim, and we can reasonably suppose that they were independent.

Suetonius apparently did have an agenda in the Twelve Caesars. This from the University of Exeter:

This module will study Suetonius Lives of the Caesars in detail, examining how the author uses the ancient genre of biography to explore the question of what it means to be a Roman Emperor, and how this changes from the 1st century BC and the dictatorship of Julius Caesar, through the rule of the Julio-Claudian and Flavian emperors to his own day. Through close analysis of passages from the set text we will explore how the author uses standard and recurrent motifs and themes such as building programmes, family relationships, death scenes, military campaigns, and sexual behaviour to characterise emperors as good or bad rulers, and investigate how he writes about the private lives of public figures as a way of thinking about the nature of power itself. (

In other words it's understood that Suetonius paints each ruler into the corner of what he believed to be either a “good” one or a “bad” one. It follows from this that if Suetonius thought Caesar was a “good” ruler he would be inclined to interpret evidence to favor his bias toward Caesar. This polemical theme could explain why Suetonius would be inclined to report that Cicero – a man that rejoiced in Caesar’s assassination and hated his politics – also spoke so glowingly of Caesar’s biased memoirs which documented his military success. Which on the face of it seems counterintuitive.

I never said he had no agenda. I said that nothing we know about his agenda would have made him unduly credulous about Caesar’s authorship of the Gallic Wars. Your speculation that he would have trusted Cicero just because Cicero hated Caesar is a reach. Besides, it doesn’t change the facts that (1) Suetonius tells us that he did use Cicero as a source and (2) Cicero actually was in a position to know whether Caesar wrote the Gallic Wars. Irenaeus tells us nothing about his source. At least in the case of Luke’s gospel, he doesn’t even say he had a source. For all we can infer from what he wrote, he could have been just guessing.

Further, Suetonius' reliability as a historian is debatable. He reported omens and signs such a seven day comet which was believed to be Caesars soul rising to heaven. On some points he flat out contradicts earlier biographers of Caesar such as Plutarch. Lastly, Suetonius was fond of reporting hearsay in the form of “everyone knows.”

You are misconstruing my argument. I am not saying, “Suetonius said it, I believe it, and that settles it.” I am explaining why I feel justified in thinking that Irenaeus is not as good a source as Suetonius is, on this one issue of who wrote a particular book.

I note here you argue the Anti-Marcionite prologue’s source “could have been” Ireneaus, thereby discounting it even though the prologue itself doesn’t tell us its source. A few moments later in the same post you argue I can’t properly infer Irenaeus’ source was Polycarp because Irenaeus doesn’t explicitly say it was Polycarp. So, on the one hand when it suits you the mere possibility that a source “could have” used Irenaeus is enough to discard that source. But when it comes to Irenaeus possibly having Polycarp as his source that doesn’t work because Irenaeus doesn’t explicitly state Polycarp was his source. You are arguing out of both sides of your mouth.

The issue with the Anti-Marcionite prologue is its independence, which cannot be assumed. It has to be demonstrated. The issue with Irenaeus is whether we have good reason to think he had a source that we should trust for his particular statement about the authorship of Luke’s gospel. He does not identify his source for that datum, and since we don’t know his source, we cannot have a good reason to trust that source.

Like the Anti-Marcionite prologue the Bodmer Papyrus is a source that comes in well under the 170 year marker even if we give the later date of c. 225AD. It is therefore admissible as a source.

You are arguing in effect, “Suetonius wrote 170 years after Caesar, and we trust him, and so we should trust anybody testifying to Lucan authorship within 170 years of its alleged composition date.” That’s ridiculous. I am aware of no historiographical principle that says we must give equal credibility to all sources written within X years of the events they report. Nor have I have until now seen it alleged, by any other evangelical apologist, that there is such a principle.

Granted, there is a principle, widely accepted by both secular and Christian scholars, that earlier sources are to be preferred over later sources, all else being equal. But the equality must include subject matter. If Caesar's authorship of the Gallic Wars were disputed, and if any source earlier than Suetonius were to contradict him, then we would have a prima facie case for thinking Suetonius was mistaken. This in no way implies that just because Irenaeus was chronologically closer to Luke than Suetonius was to Caesar, we should give him at least as much credence as we give Suetonius. Credibility is not a function solely of absolute time elapsed between subject and source, and no real historian says it is.

You did not prove that Cicero, Hirtius and Pollio are independent but rather merely assumed they are.

Show me why it would be reasonable to suspect the contrary. If two of them are dependent, then they believed it just on the say-so of the third. That is not a credible scenario if there is no evidence to support it. Since they all knew Caesar, they at least had independent access to the fact at issue. It is of course possible that only one of them had actual knowledge of whether Caesar wrote the Gallic Wars and the other two simply took his word for it without confirming it for themselves. That still gives us two men who knew Caesar and who, having been told that he wrote the book in question, ought to have known whether there was any reason to doubt it.

You asserted earlier there were three contemporary sources attesting to Caesar’s authorship with Cicero, Hirtius and Pollio.

No, I didn’t assert that. I asserted that Suetonius identified three sources who were contemporaries of Caesar, in contrast to Irenaeus, who identified no sources.

Suetonius doesn’t quote anything from Pollio but rather simply gives his interpretation of what he thinks Pollio said about Caesar’s memoirs. Since you discount Irenaeus’ letter to Florinus because the letter no longer exists we can likewise discount Pollio as none of his work is extant either. That eliminates Pollio from the discussion.

Not quite. I’m not comparing Pollio with anybody, because there is nobody to compare him with. I am comparing Suetonius with Irenaeus. Suetonius identifies Pollio as a source. Irenaeus identifies nobody as a source.

Hirtius and Cicero write virtually the same thing in their respective quotes given by Suetonius. To use your reasoning Cicero “could have” been paraphrasing Hirtius or Hirtius “could have” been paraphrasing Cicero. In either case because their quotes are so very similar we must conclude one was borrowing from the other. Isn’t that right?

No, it isn’t. They are not “virtually the same thing.” They are no more similar than any two independently written book reviews you might see nowadays.

You must have missed the part in Irenaeus’ letter to Florinus where he says in regards to his experiences with Polycarp, “I remember the events of that time more clearly than those of recent years.”

I didn’t miss anything. I’m just not taking an old man’s word for it that I should trust his memories of youth any more than I can trust my own.

Your argument that Irenaeus and Eusebius “would have said so” if Polycarp had told Irenaeus who wrote the Gospels is nothing more than an argument from silence.

Of course it is. There are good arguments from silence, and this is one of them. It is reasonable to believe that Irenaeus would have made a big deal of having gotten that information from a source of that kind and that Eusebius would have mentioned his having done so.

Irenaeus’ certainty about the authorship of the gospels is itself evidence that he had a reliable source in Polycarp.

It is nothing of the sort. This is in effect the fallacy of affirming the consequent. If Irenaeus’s source actually was Polycarp, and if Polycarp actually did know the apostle John, and if Polycarp did tell Irenaeus that Luke wrote a gospel, then yes, Irenaeus would have felt very certain about who wrote that gospel. But the converse does not follow.

Concluding remarks:

Evidence for any hypothesis comes in degrees of sufficiency, and sufficiency is an inverse measure of the probability that the hypothesis could be false notwithstanding the particular facts offered in evidence. In this exercise we are comparing (1) the probability that Suetonius would have said Caesar wrote the Gallic Wars had Caesar not actually done so with (2) the probability that Irenaeus would have said a companion of Paul wrote Luke's gospel had that companion not actually done so. My argument is that the first probability is considerably less than the second, and I am not disregarding any of the apologist's evidence in doing so. I am not denying that it is evidence. I am simply denying that it proves as much as the apologist says it proves. Irenaeus's testimony is evidence that the author of Luke's gospel was a companion of Paul. But it is not good evidence. The reason it is not good, is that neither Irenaeus himself nor anyone else provides us with any information that would justify our thinking it unlikely that he was mistaken about the gospel's authorship.

Suetonius, on the other hand, does gives us a reason to think he was probably not mistaken. He tells us of his familiarity with three writers, all acquaintances of Caesar, who affirm Caesar's authorship of the Gallic Wars. Could he still have been mistaken? Absolutely. Unlike apologists, secular historians don't treat any source as infallible. The probability that Suetonius was wrong is not zero, and new evidence could give us good reason to think it’s way above zero. But we haven't found that evidence yet, and until we do, we're justified in thinking that his probability of error is far lower than Irenaeus's.

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(This page last updated on January 5, 2015.)