Authority, concensus, bias and ad homs

I have been debating with Rob Martin on his site here, here, and here, his response to Richard Carrier’s mythicist claims.  I think it is worth setting out here my full response to the issues raised in those discussions, because they are so fundamental to how we argue validly (or not).*

We need to understand the following concepts:

A – A valid appeal to authority.

B – A dispute as to the expertise of the alleged authority

C- An attack on a the truth or reliability of any argument by attacking the person who is putting the argument forward. 

A and  B are perfectly acceptable as far as they go.  The problem is that they don’t go very far. C is always fallacious. 

Appeal to Authority 

An appeal to authority can validly be used when we are trying to determine something outside our own field of knowledge.  For instance, not being able to read Ancient Greek myself, I have to rely on those who can if any issue involving an Ancient Greek text arises. 

But it is important to remember the limitations on the Appeal to Authority. First of all, it cannot be used as logical proof.  It can never follow as a matter of deductive logic that because an expert (or hundreds of experts for that matter) hold a particular opinion, that opinion must be right. Experts can and have in the past been wrong, including on matters where they were all at one time in agreement.

However,  the fact that A, who is an expert in a certain field, believes x to be the case is some evidence that x is indeed the case, provided that:

  1. A’s expertise is relevant to the issue of x’s truthfulness.
  2. A is not biased
  3. A’s opinion is not unrepresentative of the view taken by the majority of experts in the same field.

It would be a logical fallacy to argue deductively:

  • A says that x is true.
  • A is an expert about x (and none of the disqualifying factors at 1 – 3 above apply)
  • Therefore x is true.

In order for the argument to be logically sound, we would have to insert a further premise:

  • Experts are invariably right in their field of expertise. 

But that premise is clearly wrong.  In the field of astro-physics it was at one time the majority view amongst experts that the universe had always existed in (more or less) its present form (the Steady State Theory). These days the majority of experts believe that the universe did not always exist in its present state (the Big Bang Theory). They cannot both be right and so it follows that the fact the majority, even the overwhelming majority, of experts in a particular field hold x to be true is not logical proof that x is in fact true. 

But what we can do with expert testimony is use it inductively as evidence.  We may argue inductively (with another lay person) as follows:

  • A says that x is true.
  • A is an expert about x (and none of the disqualifying factors at 1 – 3 above apply).
  • Therefore it is reasonable for us to believe that x is true. 

So, in the case of Richard Carrier, if Anne argues that Jesus is a myth because Richard Carrier says so, then her appeal to authority is unreasonable and her conclusion is not only logically unsound but is evidentially weak.  This is because, although Richard Carrier is an expert in this field, his views are not representative of the scholarly concensus in that field.

However, and I cannot emphasise this enough, this is not any kind of argument against Richard Carrier’s stance. It operates only as a rejection of Anne’s argument that she had proved that Jesus was a myth, simply by virtue of Carrier’s opinion. It does not help us at all with deciding whether or not Carrier is actually right.  We have refuted Anne, not Carrier himself. 

Disputing the Expertise of the Alleged Authority 

This happens when we raise any of the factors at 1, 2 or 3 above in response to an appeal to authority. If we can successfully show that one or more of those factors applies to the expert, then their opinion should carry no weight.  Our opponent has lost their expert witness but they have not lost the argument, which must continue on its own merits. 

Ad Hominem

Actually, I see no good reason to think Carrier is biased on the question of Jesus’ historicity, but let us assume for the present purposes that he is.  In fact, let us assume that no historian ever has he been or ever will be as biased on any topic as Carrier is on this.  Let us assume that Carrier is utterly driven to disprove the historical existence of Jesus to the extent that he can never know a moment’s peace until he has done so to his own satisfaction.  If this is assumed, what affect should it have on our assessment of his arguments?

None.  Zip. Nada. Nil.

To believe otherwise is to fall into the ad Hominem fallacy. 

It wholly discredits him as an expert.  But then again, he was already disqualified as an expert by virtue of  factor 3 above so the mythicist claim is no weaker than it was to start with and the historicist claim is no further forward. 

I hope that’s clear. 

*Since this blog was written but before it was posted, Rob has replied to my comments on the two most recent threads to which I’ve linked.  He is always a thoughtful and gracious opponent.