Credo Ut Intelligam

Interesting blog, Sir. I hope you don't mind an intrusion.

Incoherent... compared to what? When Van Til speaks of this, he does give reference to said incoherence. The worldly position, whatever it may be, is not coherent when compared to the Christian position, which is a true position. But, when compared to particular imperical evidence, the worldly position may indeed be quite coherent.

I don't think that you are saying much that differs from Van Til, but rather are comparing relative perspectives. Let's look for a moment at another kind of apologietic- variations of doctrine among Christians. The Van Tillian argument, as you have posited, would apply, because both parties agree on the first point. therefore, demonstrating worldly arguments from reductiones ad absurdam would be applicable. On the other hand, the non-Christian, using your argument, may not agree to the first point, but may indeed agree on the second or even the conclusion. Consider this argument:

1) Christianity is true
2) If Christianity is true then all non-Christian faiths are not rational
3) Therefore all non-Christian faiths are not rational

Any construct whose premise is not true will, regardless of cohesion or logical consistency, be irrational. Irrationality, given sufficient rope to draw its ultimate logical conclusions, will lead to non-reason. I tend to think that Van Til had this in mind to some extent when he wrote of reductiones ad absurdam in apologetics. However, I agree that cohesion is not the problem. Rather, it is rationality.

I do look forward to continued discussion. If you don't mind, I'd like to put your site amongs't the links on my blog.

Theognome

If this is the case, that non-Christian systems can be internally coherent then there is no effective way to apologize. If their system is coherent, complete (and I use this word loosely because no one will ever admit their system cannot be improved upon), without fallacy then it becomes unassailable. If the Christian is not willing to argue that Christianity is the only complete, infallible system then the Christian has lost before he has started.

Reading through Greg Bahnsen's "Van Til's Apologetic" makes it emmensely more clear that at the heart of presuppositionalism is the belief that only the Christian worldview will give an individual a coherent interpretation of reality that is totally complete (even if we don't have it completely figured out) and without error. If you are going to cling to the adage that "all truth is God's truth" then it becomes unavoidable for every non-Christian system to, as Bahnsen and Van Til would say, borrow from the Christian worldview. They would argue that neutrality is an impossibility and that, unlike what traditional or classical apologetics maintain, there is no level battlefield; no place where the Christian and the non-Christian can meet as equals and work out their systems to see who's is better.

Of course, personally, I would argue that the best way to apologize is to be affective, not necessarily effective...

I can see the overall point in your criticism of Van Tillian apologetics, but I do have a couple of differences. First, you say, "Well, if we can show that all non-Christian thought is internally incoherent, isn’t that a proof of Christianity? Not a direct proof, to be sure, but a proof nonetheless." Actually, the demonstration that all non-Christian thought is incoherent does nothing to show that Christian thought is not itself also incoherent. Second, your distinction between non-Christian persons and non-Christian belief systems is valid. However, does not the premise that all non-Christians hold to a belief in Jehovah, regardless of whether they will admit to it, demonstrate that the belief system itself is also invalid, since this unacknowledged belief is now a part of the system? It seems to be the point of presuppositionalism that it is precisely this borrowing of Christian capital by non-Christians that is the chief cause of the incoherence in their belief systems. Were it not for this, then I agree that many of these belief systems are coherent.

Kevin, the unacknowledged belief in Jehovah is by definition not part of an atheistic system. A person's system is whatever he admits to believing (that's just what I mean by 'system').

And if all non Christian though is incoherent then the proposition "Christianity is false" is false. Therefore Christianity is true. Therefore Christianity is coherent.

Can rationality, all by itself, discover any and every truth?

If not, then not every construct whose premise is false will be irrational.

I understand your first explanation and, rereading your post, it makes sense in the context. The second one isn't so clear. First, it appears to prove too much. One could also say, "If all non Christian thought is incoherent then the proposition "Islam is false" is false. Therefore Islam is true. Therefore Islam is coherent." Or,"If all non Christian thought is incoherent then the proposition "Christianity is true" is false. Therefore Christianity is false. Therefore Christianity is incoherent." This might work as a reductio ad absurdam against Van Til's claim, but, to me, it looks more like a case of linguistic prestidigitation.

Second, it seems to be a non sequiter. Your statement, "If all non Christian thought is incoherent then the proposition "Christianity is false" is false," appears to assume a reverse connection between propositions within incoherent thought and the actual state of affairs. It seems more to the point that incoherent thought would have no connection to the way things really are. The proposition "Christianity is false" spoken in such a context is neither false nor true, but meaningless. Consequently, it cannot serve as proof of either Christianity's veracity or its coherence.

If x is incoherent then x is false.

This is just a statment of how reductio ad absurdam works. If by assuming that x is true (it's not really true, but pretend it is) we can derive an absurdity, then our original assumption must be false: x is not true. Therefore x is false. Therefore the opposite of x is true.

You seem to think I'm arguing: x is incoherent therefore everything is incoherent. Therefore everything is false. That is invalid. The only thing that must be false if x is incoherent is x itself.

I can follow this sequence in your argument:
"The proposition 'Christianity is false' is false. Therefore Christianity is true. Therefore Christianity is coherent." But I don't see how the premise, "The proposition 'Christianity is false' is false," is a necessary conclusion to your first condition, "If all non Christian thought is incoherent."

The only connection I could see would be if any proposition made within the context of incoherent thought must also be incoherent. Couple that with the premise opening your last comment, "If x is incoherent then x is false," and your conclusion, "The proposition 'Christianity is false' is false," follows.

However, I still have a question about the premise that incoherency implies falseness. I think I demonstrated this by pointing out the possible substitution of Islam in your conclusion. This is an example in which a true statement exists within a context of supposedly non-coherent thought. This brings at least one of the premises into question. Either an incoherent thought context does not imply that a proposition within that context is also incoherent, in which case the incoherence and, consequently, the falsity of the proposition, "Christianity is false," would not follow from the fact that it was spoken within an incoherent context. Or, incoherency does not imply falseness, in which case the incoherency of the proposition, "Christianity is false," may follow from its incoherent context, but the falsity of this same proposition could not also be deduced from its incoherent context. I'm really not sure which way to go on this. Either way, the falseness of the proposition, "Christianity is false," would appear to have nothing to do with whether or not all non-Christian thought is incoherent. And because of this, it has not been demonstrated that the incoherency of non-Christian thought proves the coherency or veracity of Christian thought.

The situation is far more simple than you're making it.

To say that all non-Christian thought is incoherent means that the proposition "Christianity is false" leads to an absurdity no matter what other propositions we put around it. Suppose a non-Christian system contains two propositions, "Christianity is false," and p. Another non-Christian system contains only "Christianity is false" and not-p. If every non-Christian system is incoherent, then both of those systems are incoherent, so they are both false. But the the law of excluded middle says that either p or not-p is true. Therefore "Christianity is false" is false.

In symbols, ~(x &p)&~(x&~p) --> ~x, where x="Christianity is false".

I leave for homework the task of extending this analysis to non-Christian systems containing three propositions

I also leave for homework the task of extending this analysis to non-Christian systems containing four propositions

I also leave for homework the task of ...

Regarding Islam: You didn't substitute correctly. The argument-form is:

All non-X thought is incoherent
Therefore "X is false" is false
Therefore X is true

substituting "Islam" for X, we get:
1) All non-Islamic thought is incoherent
2) Therefore "Islam is false" is false
3) Therefore Islam is true.

This is a valid argument with a false premise.

Okay, I get the symbols, but, before accepting the conclusion, I need to be shown how incoherency implies falseness. [My own intuition tells me that it doesn't; unfortunately, I have already rejected intuiton in our exchange over on my blog.] As to the Islam substitution, I wasn't thinking of "All non-X thought is incoherent," as a part of the argument but as descriptive of the supposed context in which the subsequent argument was made. Obviously, this is not what you meant. Still, I need an argument to the effect that incoherent implies false before I can agree that 1) implies 2).

You're pulling my leg, right? ... OK, I'll play along:

A system of propositions is incoherent if and only if it entails a logical contradiction or some other absurdity. This means that a reductio ad absurdam can be constructed against the system. So if S is incoherent then I can prove that S is false by using reductio ad absurdam. If I can prove that S is false then S is false.

By the way, Kevin, have you finnished your infinite homework assigment yet? ;-)

But a system cannot be true or false. This distinction applies only to the propositions within the system. The coherency of a system has to do with the interrelationship of its propositions: do its conclusions follow from its premises? It is possible to have an incoherent system in which all of the propositions are true; or a coherent system in which all the propositions are false.

A reductio ad absurdam is used to demonstrate that something is false. A reductio cannot be constructed against something that is true and not false, nor can it be constructed against something that is incapable of being true or false.

Your symbolic argument, ~(x &p)&~(x&~p) --> ~x, is confusing the coherency of a system with the veracity of a conjunctive proposition. I agree that ~x; however, this conclusion cannot be derived by contrasting two incoherent systems. Before it is possible to say, ~(x &p)&~(x&~p), it needs to be established that (x &p) and (x&~p) are not contradictory. If they are, then (x &p)or (x&~p)-->x. It is necessary to assume a conclusion that is not a part of either of the represented systems, namely, ~x. The argument would look like this: ~x --> ~((x &p)or (x&~p))-->~(x &p)&~(x&~p). The only proof has been by the law of non-contradiction where ~x, insofar as it is true, has shown the proposition x to be false. ~x has not proven the incoherency of the systems, nor has the incoherency of the systems proven ~x.

An ARGUMENT (not a system) whose conclusion follows from its premises is VALID (not coherent). A SYSTEM consists of propositions a person admits to believing, so that while not everything a person believes is at the level of his system, whatever is in the system is a proposition he believes (this is what I mean by 'system'). A system may, and usually does, contain propositions about arguments as well as propositions about other propositions. I call a system FALSE if the conjunction of all propositions contained in it is false (this is just what I mean when I say a system is false). I call a system INCOHERENT iff the propositions contained in it lead to a contradiction or other absurdity (this is just what I mean by 'incoherent'). From these DEFINITIONS it follows that an incoherent system is false, and if all systems containing x are incoherent then x is false.

I've been thinking of systems and coherency in terms analogous to arguments and validity. Evidently, our definitions have not been the same. I guess the question in the original context of your bringing it up would be how Van Til defines a system.

Suppose I accept your definition of a false system, "I call a system FALSE if the conjunction of all propositions contained in it is false." A conjunction of propositions is true iff each and every proposition within that conjuction is true. It only takes a single false proposition to make a conjunction of propositions false. Why couldn't x be a true proposition within a conjunction of propositions that is false?

Which leads to your definition of an incoherent system, "I call a system INCOHERENT iff the propositions contained in it lead to a contradiction or other absurdity." But the very existence of a contradiction presupposes the presence of a true proposition. A contradiction can only exist between what is true and what is false. If every proposition within a system were false, then incongruent propositions within that system could only be regarded as contrary, not as contradictory. So, in a system that leads to a contradiction, why couldn't x be true?

You are correct to point out that just because x occurs in an incoherent system does not imply that it is false. However, if every possible system in which x occurs is incoherent then x is false. If x is true, then we can put as many true propositions around it as we like and we're never going to get a contradiction (any conjunction of true propositions is non-contradictory). So if x is true there exists a consistent system containing x. But VanTil pretends to show that that there does not exist such a system. He often cashes this out by saying that non-Christians systems make morality, rationality, etc. unintelligible, implying that this is an absurdity. If the system in question also contains the proposition that morality, rationality, etc. are intelligible then it is a contradition.

I think I can always turn your kind of system into my kind: If A is a system in your sense, thought of as a great big argument, then the proposition "A is a sound argument" can be a system in my sense.

Okay, you win. I was thinking in terms of all extant non-Christian systems, which would not deny the possibility of a non-Christian system that was coherent. However, if Van Til is saying that non-Christian systems, by definition, are incoherent, then this would cover all possibilities. Since all possible non-Christian systems contain x, then x would have to be false. It is a proof for ~x, but just a bit too circular for my taste.

The problem with assuming an all possible worlds argument for non-Christian incoherency is that you can never get the opposition to agree. A lot of presuppositional apologetics is done by demolishing a particular non-Christian system. Christianity is then, supposedly, true by default. However, unless someone is convinced that there cannot exist another, as yet undiscovered, non-Christian system that is coherent, he will have little reason to accept ~x. Thanks for taking the time to explain your point.